This filter applies an exponential moving average to a sequence of audio
+ * signal values, making it useful for smoothing out rapid fluctuations.
+ * The smoothing factor (alpha) controls the degree of smoothing.
+ *
+ *
Based on the definition from
+ * Wikipedia link.
+ */
+public class EMAFilter {
+ private final double alpha;
+ private double emaValue;
+ /**
+ * Constructs an EMA filter with a given smoothing factor.
+ *
+ * @param alpha Smoothing factor (0 < alpha <= 1)
+ * @throws IllegalArgumentException if alpha is not in (0, 1]
+ */
+ public EMAFilter(double alpha) {
+ if (alpha <= 0 || alpha > 1) {
+ throw new IllegalArgumentException("Alpha must be between 0 and 1.");
+ }
+ this.alpha = alpha;
+ this.emaValue = 0.0;
+ }
+ /**
+ * Applies the EMA filter to an audio signal array.
+ *
+ * @param audioSignal Array of audio samples to process
+ * @return Array of processed (smoothed) samples
+ */
+ public double[] apply(double[] audioSignal) {
+ if (audioSignal.length == 0) {
+ return new double[0];
+ }
+ double[] emaSignal = new double[audioSignal.length];
+ emaValue = audioSignal[0];
+ emaSignal[0] = emaValue;
+ for (int i = 1; i < audioSignal.length; i++) {
+ emaValue = alpha * audioSignal[i] + (1 - alpha) * emaValue;
+ emaSignal[i] = emaValue;
+ }
+ return emaSignal;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/audiofilters/IIRFilter.java b/src/main/java/com/thealgorithms/audiofilters/IIRFilter.java
index 0de145f60c67..fbc095909541 100644
--- a/src/main/java/com/thealgorithms/audiofilters/IIRFilter.java
+++ b/src/main/java/com/thealgorithms/audiofilters/IIRFilter.java
@@ -4,7 +4,7 @@
* N-Order IIR Filter Assumes inputs are normalized to [-1, 1]
*
* Based on the difference equation from
- * https://en.wikipedia.org/wiki/Infinite_impulse_response
+ * Wikipedia link
*/
public class IIRFilter {
@@ -58,7 +58,7 @@ public void setCoeffs(double[] aCoeffs, double[] bCoeffs) throws IllegalArgument
throw new IllegalArgumentException("bCoeffs must be of size " + order + ", got " + bCoeffs.length);
}
- for (int i = 0; i <= order; i++) {
+ for (int i = 0; i < order; i++) {
coeffsA[i] = aCoeffs[i];
coeffsB[i] = bCoeffs[i];
}
diff --git a/src/main/java/com/thealgorithms/backtracking/AllPathsFromSourceToTarget.java b/src/main/java/com/thealgorithms/backtracking/AllPathsFromSourceToTarget.java
index 8122ed4dd0c6..6f93b704ffb2 100644
--- a/src/main/java/com/thealgorithms/backtracking/AllPathsFromSourceToTarget.java
+++ b/src/main/java/com/thealgorithms/backtracking/AllPathsFromSourceToTarget.java
@@ -1,19 +1,18 @@
-/**
- * Author : Siddhant Swarup Mallick
- * Github : https://github.com/siddhant2002
- */
-
-/** Program description - To find all possible paths from source to destination*/
-
-/**Wikipedia link -> https://en.wikipedia.org/wiki/Shortest_path_problem */
package com.thealgorithms.backtracking;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.List;
+/**
+ * Program description - To find all possible paths from source to destination
+ * Wikipedia
+ *
+ * @author Siddhant Swarup Mallick
+ */
public class AllPathsFromSourceToTarget {
// No. of vertices in graph
- private int v;
+ private final int v;
// To store the paths from source to destination
static List> nm = new ArrayList<>();
@@ -89,8 +88,8 @@ private void storeAllPathsUtil(Integer u, Integer d, boolean[] isVisited, List> allPathsFromSourceToTarget(int vertices, int[][] a, int source, int destination) {
// Create a sample graph
AllPathsFromSourceToTarget g = new AllPathsFromSourceToTarget(vertices);
- for (int i = 0; i < a.length; i++) {
- g.addEdge(a[i][0], a[i][1]);
+ for (int[] i : a) {
+ g.addEdge(i[0], i[1]);
// edges are added
}
g.storeAllPaths(source, destination);
@@ -98,4 +97,4 @@ public static List> allPathsFromSourceToTarget(int vertices, int[]
return nm;
// returns all possible paths from source to destination
}
-}
\ No newline at end of file
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/ArrayCombination.java b/src/main/java/com/thealgorithms/backtracking/ArrayCombination.java
index 50ef8f7234de..f8cd0c40c20e 100644
--- a/src/main/java/com/thealgorithms/backtracking/ArrayCombination.java
+++ b/src/main/java/com/thealgorithms/backtracking/ArrayCombination.java
@@ -1,29 +1,54 @@
package com.thealgorithms.backtracking;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.List;
/**
- * Finds all permutations of 1...n of length k
- * @author TheClerici (https://github.com/TheClerici)
+ * This class provides methods to find all combinations of integers from 0 to n-1
+ * of a specified length k using backtracking.
*/
-public class ArrayCombination {
- private static int length;
+public final class ArrayCombination {
+ private ArrayCombination() {
+ }
+
+ /**
+ * Generates all possible combinations of length k from the integers 0 to n-1.
+ *
+ * @param n The total number of elements (0 to n-1).
+ * @param k The desired length of each combination.
+ * @return A list containing all combinations of length k.
+ * @throws IllegalArgumentException if n or k are negative, or if k is greater than n.
+ */
+ public static List> combination(int n, int k) {
+ if (n < 0 || k < 0 || k > n) {
+ throw new IllegalArgumentException("Invalid input: n must be non-negative, k must be non-negative and less than or equal to n.");
+ }
+
+ List> combinations = new ArrayList<>();
+ combine(combinations, new ArrayList<>(), 0, n, k);
+ return combinations;
+ }
/**
- * Find all combinations of 1..n by creating an array and using backtracking in Combination.java
- * @param n max value of the array.
- * @param k length of combination
- * @return a list of all combinations of length k. If k == 0, return null.
+ * A helper method that uses backtracking to find combinations.
+ *
+ * @param combinations The list to store all valid combinations found.
+ * @param current The current combination being built.
+ * @param start The starting index for the current recursion.
+ * @param n The total number of elements (0 to n-1).
+ * @param k The desired length of each combination.
*/
- public static List> combination(int n, int k) {
- if (n <= 0) {
- return null;
+ private static void combine(List> combinations, List current, int start, int n, int k) {
+ // Base case: combination found
+ if (current.size() == k) {
+ combinations.add(new ArrayList<>(current));
+ return;
}
- length = k;
- Integer[] arr = new Integer[n];
- for (int i = 1; i <= n; i++) {
- arr[i - 1] = i;
+
+ for (int i = start; i < n; i++) {
+ current.add(i);
+ combine(combinations, current, i + 1, n, k);
+ current.remove(current.size() - 1); // Backtrack
}
- return Combination.combination(arr, length);
}
-}
\ No newline at end of file
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/Combination.java b/src/main/java/com/thealgorithms/backtracking/Combination.java
index 70ae32b5c17f..ecaf7428f986 100644
--- a/src/main/java/com/thealgorithms/backtracking/Combination.java
+++ b/src/main/java/com/thealgorithms/backtracking/Combination.java
@@ -1,14 +1,18 @@
package com.thealgorithms.backtracking;
-import java.util.*;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.TreeSet;
/**
* Finds all permutations of given array
- * @author Alan Piao (https://github.com/cpiao3)
+ * @author Alan Piao (git-Alan Piao)
*/
-public class Combination {
-
- private static int length;
+public final class Combination {
+ private Combination() {
+ }
/**
* Find all combinations of given array using backtracking
@@ -18,37 +22,45 @@ public class Combination {
* @return a list of all combinations of length n. If n == 0, return null.
*/
public static List> combination(T[] arr, int n) {
+ if (n < 0) {
+ throw new IllegalArgumentException("The combination length cannot be negative.");
+ }
+
if (n == 0) {
- return null;
+ return Collections.emptyList();
}
- length = n;
T[] array = arr.clone();
Arrays.sort(array);
+
List> result = new LinkedList<>();
- backtracking(array, 0, new TreeSet(), result);
+ backtracking(array, n, 0, new TreeSet(), result);
return result;
}
/**
* Backtrack all possible combinations of a given array
* @param arr the array.
+ * @param n length of the combination
* @param index the starting index.
* @param currSet set that tracks current combination
* @param result the list contains all combination.
* @param the type of elements in the array.
*/
- private static void backtracking(T[] arr, int index, TreeSet currSet, List> result) {
- if (index + length - currSet.size() > arr.length) return;
- if (length - 1 == currSet.size()) {
+ private static void backtracking(T[] arr, int n, int index, TreeSet currSet, List> result) {
+ if (index + n - currSet.size() > arr.length) {
+ return;
+ }
+ if (currSet.size() == n - 1) {
for (int i = index; i < arr.length; i++) {
currSet.add(arr[i]);
- result.add((TreeSet) currSet.clone());
+ result.add(new TreeSet<>(currSet));
currSet.remove(arr[i]);
}
+ return;
}
for (int i = index; i < arr.length; i++) {
currSet.add(arr[i]);
- backtracking(arr, i + 1, currSet, result);
+ backtracking(arr, n, i + 1, currSet, result);
currSet.remove(arr[i]);
}
}
diff --git a/src/main/java/com/thealgorithms/backtracking/CrosswordSolver.java b/src/main/java/com/thealgorithms/backtracking/CrosswordSolver.java
new file mode 100644
index 000000000000..6bfb026c7de9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/CrosswordSolver.java
@@ -0,0 +1,125 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * A class to solve a crossword puzzle using backtracking.
+ * Example:
+ * Input:
+ * puzzle = {
+ * {' ', ' ', ' '},
+ * {' ', ' ', ' '},
+ * {' ', ' ', ' '}
+ * }
+ * words = List.of("cat", "dog")
+ *
+ * Output:
+ * {
+ * {'c', 'a', 't'},
+ * {' ', ' ', ' '},
+ * {'d', 'o', 'g'}
+ * }
+ */
+public final class CrosswordSolver {
+ private CrosswordSolver() {
+ }
+
+ /**
+ * Checks if a word can be placed at the specified position in the crossword.
+ *
+ * @param puzzle The crossword puzzle represented as a 2D char array.
+ * @param word The word to be placed.
+ * @param row The row index where the word might be placed.
+ * @param col The column index where the word might be placed.
+ * @param vertical If true, the word is placed vertically; otherwise, horizontally.
+ * @return true if the word can be placed, false otherwise.
+ */
+ public static boolean isValid(char[][] puzzle, String word, int row, int col, boolean vertical) {
+ for (int i = 0; i < word.length(); i++) {
+ if (vertical) {
+ if (row + i >= puzzle.length || puzzle[row + i][col] != ' ') {
+ return false;
+ }
+ } else {
+ if (col + i >= puzzle[0].length || puzzle[row][col + i] != ' ') {
+ return false;
+ }
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Places a word at the specified position in the crossword.
+ *
+ * @param puzzle The crossword puzzle represented as a 2D char array.
+ * @param word The word to be placed.
+ * @param row The row index where the word will be placed.
+ * @param col The column index where the word will be placed.
+ * @param vertical If true, the word is placed vertically; otherwise, horizontally.
+ */
+ public static void placeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
+ for (int i = 0; i < word.length(); i++) {
+ if (vertical) {
+ puzzle[row + i][col] = word.charAt(i);
+ } else {
+ puzzle[row][col + i] = word.charAt(i);
+ }
+ }
+ }
+
+ /**
+ * Removes a word from the specified position in the crossword.
+ *
+ * @param puzzle The crossword puzzle represented as a 2D char array.
+ * @param word The word to be removed.
+ * @param row The row index where the word is placed.
+ * @param col The column index where the word is placed.
+ * @param vertical If true, the word was placed vertically; otherwise, horizontally.
+ */
+ public static void removeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
+ for (int i = 0; i < word.length(); i++) {
+ if (vertical) {
+ puzzle[row + i][col] = ' ';
+ } else {
+ puzzle[row][col + i] = ' ';
+ }
+ }
+ }
+
+ /**
+ * Solves the crossword puzzle using backtracking.
+ *
+ * @param puzzle The crossword puzzle represented as a 2D char array.
+ * @param words The list of words to be placed.
+ * @return true if the crossword is solved, false otherwise.
+ */
+ public static boolean solveCrossword(char[][] puzzle, Collection words) {
+ // Create a mutable copy of the words list
+ List remainingWords = new ArrayList<>(words);
+
+ for (int row = 0; row < puzzle.length; row++) {
+ for (int col = 0; col < puzzle[0].length; col++) {
+ if (puzzle[row][col] == ' ') {
+ for (String word : new ArrayList<>(remainingWords)) {
+ for (boolean vertical : new boolean[] {true, false}) {
+ if (isValid(puzzle, word, row, col, vertical)) {
+ placeWord(puzzle, word, row, col, vertical);
+ remainingWords.remove(word);
+ if (solveCrossword(puzzle, remainingWords)) {
+ return true;
+ }
+ remainingWords.add(word);
+ removeWord(puzzle, word, row, col, vertical);
+ }
+ }
+ }
+ return false;
+ }
+ }
+ }
+ return true;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/FloodFill.java b/src/main/java/com/thealgorithms/backtracking/FloodFill.java
index b6b1c5ee19f8..c8219ca8ba7e 100644
--- a/src/main/java/com/thealgorithms/backtracking/FloodFill.java
+++ b/src/main/java/com/thealgorithms/backtracking/FloodFill.java
@@ -2,9 +2,11 @@
/**
* Java program for Flood fill algorithm.
- * @author Akshay Dubey (https://github.com/itsAkshayDubey)
+ * @author Akshay Dubey (Git-Akshay Dubey)
*/
-public class FloodFill {
+public final class FloodFill {
+ private FloodFill() {
+ }
/**
* Get the color at the given coordinates of a 2D image
@@ -14,7 +16,7 @@ public class FloodFill {
* @param y The y co-ordinate of which color is to be obtained
*/
- public static int getPixel(int[][] image, int x, int y) {
+ public static int getPixel(final int[][] image, final int x, final int y) {
return image[x][y];
}
@@ -25,7 +27,7 @@ public static int getPixel(int[][] image, int x, int y) {
* @param x The x co-ordinate at which color is to be filled
* @param y The y co-ordinate at which color is to be filled
*/
- public static void putPixel(int[][] image, int x, int y, int newColor) {
+ public static void putPixel(final int[][] image, final int x, final int y, final int newColor) {
image[x][y] = newColor;
}
@@ -38,10 +40,10 @@ public static void putPixel(int[][] image, int x, int y, int newColor) {
* @param newColor The new color which to be filled in the image
* @param oldColor The old color which is to be replaced in the image
*/
- public static void floodFill(int[][] image, int x, int y, int newColor, int oldColor) {
- if (x < 0 || x >= image.length) return;
- if (y < 0 || y >= image[x].length) return;
- if (getPixel(image, x, y) != oldColor) return;
+ public static void floodFill(final int[][] image, final int x, final int y, final int newColor, final int oldColor) {
+ if (newColor == oldColor || x < 0 || x >= image.length || y < 0 || y >= image[x].length || getPixel(image, x, y) != oldColor) {
+ return;
+ }
putPixel(image, x, y, newColor);
diff --git a/src/main/java/com/thealgorithms/backtracking/KnightsTour.java b/src/main/java/com/thealgorithms/backtracking/KnightsTour.java
index 882b43537b7f..2c2da659f3aa 100644
--- a/src/main/java/com/thealgorithms/backtracking/KnightsTour.java
+++ b/src/main/java/com/thealgorithms/backtracking/KnightsTour.java
@@ -1,33 +1,30 @@
package com.thealgorithms.backtracking;
-import java.util.*;
-
-/*
- * Problem Statement: -
-
- Given a N*N board with the Knight placed on the first block of an empty board. Moving according
- to the rules of chess knight must visit each square exactly once. Print the order of each cell in
- which they are visited.
-
- Example: -
-
- Input : N = 8
-
- Output:
- 0 59 38 33 30 17 8 63
- 37 34 31 60 9 62 29 16
- 58 1 36 39 32 27 18 7
- 35 48 41 26 61 10 15 28
- 42 57 2 49 40 23 6 19
- 47 50 45 54 25 20 11 14
- 56 43 52 3 22 13 24 5
- 51 46 55 44 53 4 21 12
-
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+/**
+ * The KnightsTour class solves the Knight's Tour problem using backtracking.
+ *
+ * Problem Statement:
+ * Given an N*N board with a knight placed on the first block, the knight must
+ * move according to chess rules and visit each square on the board exactly once.
+ * The class outputs the sequence of moves for the knight.
+ *
+ * Example:
+ * Input: N = 8 (8x8 chess board)
+ * Output: The sequence of numbers representing the order in which the knight visits each square.
*/
-public class KnightsTour {
+public final class KnightsTour {
+ private KnightsTour() {
+ }
+
+ // The size of the chess board (12x12 grid, with 2 extra rows/columns as a buffer around a 8x8 area)
+ private static final int BASE = 12;
- private static final int base = 12;
- private static final int[][] moves = {
+ // Possible moves for a knight in chess
+ private static final int[][] MOVES = {
{1, -2},
{2, -1},
{2, 1},
@@ -36,36 +33,40 @@ public class KnightsTour {
{-2, 1},
{-2, -1},
{-1, -2},
- }; // Possible moves by knight on chess
- private static int[][] grid; // chess grid
- private static int total; // total squares in chess
-
- public static void main(String[] args) {
- grid = new int[base][base];
- total = (base - 4) * (base - 4);
-
- for (int r = 0; r < base; r++) {
- for (int c = 0; c < base; c++) {
- if (r < 2 || r > base - 3 || c < 2 || c > base - 3) {
- grid[r][c] = -1;
+ };
+
+ // Chess grid representing the board
+ static int[][] grid;
+
+ // Total number of cells the knight needs to visit
+ static int total;
+
+ /**
+ * Resets the chess board to its initial state.
+ * Initializes the grid with boundary cells marked as -1 and internal cells as 0.
+ * Sets the total number of cells the knight needs to visit.
+ */
+ public static void resetBoard() {
+ grid = new int[BASE][BASE];
+ total = (BASE - 4) * (BASE - 4);
+ for (int r = 0; r < BASE; r++) {
+ for (int c = 0; c < BASE; c++) {
+ if (r < 2 || r > BASE - 3 || c < 2 || c > BASE - 3) {
+ grid[r][c] = -1; // Mark boundary cells
}
}
}
-
- int row = 2 + (int) (Math.random() * (base - 4));
- int col = 2 + (int) (Math.random() * (base - 4));
-
- grid[row][col] = 1;
-
- if (solve(row, col, 2)) {
- printResult();
- } else {
- System.out.println("no result");
- }
}
- // Return True when solvable
- private static boolean solve(int row, int column, int count) {
+ /**
+ * Recursive method to solve the Knight's Tour problem.
+ *
+ * @param row The current row of the knight
+ * @param column The current column of the knight
+ * @param count The current move number
+ * @return True if a solution is found, False otherwise
+ */
+ static boolean solve(int row, int column, int count) {
if (count > total) {
return true;
}
@@ -76,33 +77,37 @@ private static boolean solve(int row, int column, int count) {
return false;
}
- Collections.sort(neighbor, new Comparator() {
- public int compare(int[] a, int[] b) {
- return a[2] - b[2];
- }
- });
+ // Sort neighbors by Warnsdorff's rule (fewest onward moves)
+ neighbor.sort(Comparator.comparingInt(a -> a[2]));
for (int[] nb : neighbor) {
- row = nb[0];
- column = nb[1];
- grid[row][column] = count;
- if (!orphanDetected(count, row, column) && solve(row, column, count + 1)) {
+ int nextRow = nb[0];
+ int nextCol = nb[1];
+ grid[nextRow][nextCol] = count;
+ if (!orphanDetected(count, nextRow, nextCol) && solve(nextRow, nextCol, count + 1)) {
return true;
}
- grid[row][column] = 0;
+ grid[nextRow][nextCol] = 0; // Backtrack
}
return false;
}
- // Returns List of neighbours
- private static List neighbors(int row, int column) {
+ /**
+ * Returns a list of valid neighboring cells where the knight can move.
+ *
+ * @param row The current row of the knight
+ * @param column The current column of the knight
+ * @return A list of arrays representing valid moves, where each array contains:
+ * {nextRow, nextCol, numberOfPossibleNextMoves}
+ */
+ static List neighbors(int row, int column) {
List neighbour = new ArrayList<>();
- for (int[] m : moves) {
+ for (int[] m : MOVES) {
int x = m[0];
int y = m[1];
- if (grid[row + y][column + x] == 0) {
+ if (row + y >= 0 && row + y < BASE && column + x >= 0 && column + x < BASE && grid[row + y][column + x] == 0) {
int num = countNeighbors(row + y, column + x);
neighbour.add(new int[] {row + y, column + x, num});
}
@@ -110,19 +115,34 @@ private static List neighbors(int row, int column) {
return neighbour;
}
- // Returns the total count of neighbors
- private static int countNeighbors(int row, int column) {
+ /**
+ * Counts the number of possible valid moves for a knight from a given position.
+ *
+ * @param row The row of the current position
+ * @param column The column of the current position
+ * @return The number of valid neighboring moves
+ */
+ static int countNeighbors(int row, int column) {
int num = 0;
- for (int[] m : moves) {
- if (grid[row + m[1]][column + m[0]] == 0) {
+ for (int[] m : MOVES) {
+ int x = m[0];
+ int y = m[1];
+ if (row + y >= 0 && row + y < BASE && column + x >= 0 && column + x < BASE && grid[row + y][column + x] == 0) {
num++;
}
}
return num;
}
- // Returns true if it is orphan
- private static boolean orphanDetected(int count, int row, int column) {
+ /**
+ * Detects if moving to a given position will create an orphan (a position with no further valid moves).
+ *
+ * @param count The current move number
+ * @param row The row of the current position
+ * @param column The column of the current position
+ * @return True if an orphan is detected, False otherwise
+ */
+ static boolean orphanDetected(int count, int row, int column) {
if (count < total - 1) {
List neighbor = neighbors(row, column);
for (int[] nb : neighbor) {
@@ -133,17 +153,4 @@ private static boolean orphanDetected(int count, int row, int column) {
}
return false;
}
-
- // Prints the result grid
- private static void printResult() {
- for (int[] row : grid) {
- for (int i : row) {
- if (i == -1) {
- continue;
- }
- System.out.printf("%2d ", i);
- }
- System.out.println();
- }
- }
}
diff --git a/src/main/java/com/thealgorithms/backtracking/MColoring.java b/src/main/java/com/thealgorithms/backtracking/MColoring.java
new file mode 100644
index 000000000000..d0188dfd13aa
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/MColoring.java
@@ -0,0 +1,96 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Set;
+
+/**
+ * Node class represents a graph node. Each node is associated with a color
+ * (initially 1) and contains a set of edges representing its adjacent nodes.
+ *
+ * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+class Node {
+ int color = 1; // Initial color for each node
+ Set edges = new HashSet(); // Set of edges representing adjacent nodes
+}
+
+/**
+ * MColoring class solves the M-Coloring problem where the goal is to determine
+ * if it's possible to color a graph using at most M colors such that no two
+ * adjacent nodes have the same color.
+ */
+public final class MColoring {
+
+ private MColoring() {
+ } // Prevent instantiation of utility class
+
+ /**
+ * Determines whether it is possible to color the graph using at most M colors.
+ *
+ * @param nodes List of nodes representing the graph.
+ * @param n The total number of nodes in the graph.
+ * @param m The maximum number of allowed colors.
+ * @return true if the graph can be colored using M colors, false otherwise.
+ */
+ static boolean isColoringPossible(ArrayList nodes, int n, int m) {
+
+ // Visited array keeps track of whether each node has been processed.
+ ArrayList visited = new ArrayList();
+ for (int i = 0; i < n + 1; i++) {
+ visited.add(0); // Initialize all nodes as unvisited (0)
+ }
+
+ // The number of colors used so far (initially set to 1, since all nodes
+ // start with color 1).
+ int maxColors = 1;
+
+ // Loop through all the nodes to ensure every node is visited, in case the
+ // graph is disconnected.
+ for (int sv = 1; sv <= n; sv++) {
+ if (visited.get(sv) > 0) {
+ continue; // Skip nodes that are already visited
+ }
+
+ // If the node is unvisited, mark it as visited and add it to the queue for BFS.
+ visited.set(sv, 1);
+ Queue q = new LinkedList<>();
+ q.add(sv);
+
+ // Perform BFS to process all nodes and their adjacent nodes
+ while (q.size() != 0) {
+ int top = q.peek(); // Get the current node from the queue
+ q.remove();
+
+ // Check all adjacent nodes of the current node
+ for (int it : nodes.get(top).edges) {
+
+ // If the adjacent node has the same color as the current node, increment its
+ // color to avoid conflict.
+ if (nodes.get(top).color == nodes.get(it).color) {
+ nodes.get(it).color += 1;
+ }
+
+ // Keep track of the maximum number of colors used so far
+ maxColors = Math.max(maxColors, Math.max(nodes.get(top).color, nodes.get(it).color));
+
+ // If the number of colors used exceeds the allowed limit M, return false.
+ if (maxColors > m) {
+ return false;
+ }
+
+ // If the adjacent node hasn't been visited yet, mark it as visited and add it
+ // to the queue for further processing.
+ if (visited.get(it) == 0) {
+ visited.set(it, 1);
+ q.add(it);
+ }
+ }
+ }
+ }
+
+ return true; // Possible to color the entire graph with M or fewer colors.
+ }
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java b/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java
index d66d1482d83e..8247172e7ee0 100644
--- a/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java
+++ b/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java
@@ -1,152 +1,125 @@
package com.thealgorithms.backtracking;
-public class MazeRecursion {
+/**
+ * This class contains methods to solve a maze using recursive backtracking.
+ * The maze is represented as a 2D array where walls, paths, and visited/dead
+ * ends are marked with different integers.
+ *
+ * The goal is to find a path from a starting position to the target position
+ * (map[6][5]) while navigating through the maze.
+ */
+public final class MazeRecursion {
- public static void mazeRecursion() {
- // First create a 2 dimensions array to mimic a maze map
- int[][] map = new int[8][7];
- int[][] map2 = new int[8][7];
-
- // We use 1 to indicate wall
- // Set the ceiling and floor to 1
- for (int i = 0; i < 7; i++) {
- map[0][i] = 1;
- map[7][i] = 1;
- }
-
- // Then we set the left and right wall to 1
- for (int i = 0; i < 8; i++) {
- map[i][0] = 1;
- map[i][6] = 1;
- }
-
- // Now we have created a maze with its wall initialized
-
- // Here we set the obstacle
- map[3][1] = 1;
- map[3][2] = 1;
-
- // Print the current map
- System.out.println("The condition of the map： ");
- for (int i = 0; i < 8; i++) {
- for (int j = 0; j < 7; j++) {
- System.out.print(map[i][j] + " ");
- }
- System.out.println();
- }
-
- // clone another map for setWay2 method
- for (int i = 0; i < map.length; i++) {
- for (int j = 0; j < map[i].length; j++) {
- map2[i][j] = map[i][j];
- }
- }
-
- // By using recursive backtracking to let your ball(target) find its way in the
- // maze
- // The first parameter is the map
- // Second parameter is x coordinate of your target
- // Thrid parameter is the y coordinate of your target
- setWay(map, 1, 1);
- setWay2(map2, 1, 1);
+ private MazeRecursion() {
+ }
- // Print out the new map1, with the ball footprint
- System.out.println("After the ball goes through the map1，show the current map1 condition");
- for (int i = 0; i < 8; i++) {
- for (int j = 0; j < 7; j++) {
- System.out.print(map[i][j] + " ");
- }
- System.out.println();
+ /**
+ * This method solves the maze using the "down -> right -> up -> left"
+ * movement strategy.
+ *
+ * @param map The 2D array representing the maze (walls, paths, etc.)
+ * @return The solved maze with paths marked, or null if no solution exists.
+ */
+ public static int[][] solveMazeUsingFirstStrategy(int[][] map) {
+ if (setWay(map, 1, 1)) {
+ return map;
}
+ return null;
+ }
- // Print out the new map2, with the ball footprint
- System.out.println("After the ball goes through the map2，show the current map2 condition");
- for (int i = 0; i < 8; i++) {
- for (int j = 0; j < 7; j++) {
- System.out.print(map2[i][j] + " ");
- }
- System.out.println();
+ /**
+ * This method solves the maze using the "up -> right -> down -> left"
+ * movement strategy.
+ *
+ * @param map The 2D array representing the maze (walls, paths, etc.)
+ * @return The solved maze with paths marked, or null if no solution exists.
+ */
+ public static int[][] solveMazeUsingSecondStrategy(int[][] map) {
+ if (setWay2(map, 1, 1)) {
+ return map;
}
+ return null;
}
/**
- * Using recursive path finding to help the ball find its way in the maze
- * Description：
- * 1. map (means the maze)
- * 2. i, j (means the initial coordinate of the ball in the maze)
- * 3. if the ball can reach the end of maze, that is position of map[6][5],
- * means the we have found a path for the ball
- * 4. Additional Information： 0 in the map[i][j] means the ball has not gone
- * through this position, 1 means the wall, 2 means the path is feasible, 3
- * means the ball has gone through the path but this path is dead end
- * 5. We will need strategy for the ball to pass through the maze for example:
- * Down -> Right -> Up -> Left, if the path doesn't work, then backtrack
+ * Attempts to find a path through the maze using a "down -> right -> up -> left"
+ * movement strategy. The path is marked with '2' for valid paths and '3' for dead ends.
*
- * @author OngLipWei
- * @version Jun 23, 2021 11:36:14 AM
- * @param map The maze
- * @param i x coordinate of your ball(target)
- * @param j y coordinate of your ball(target)
- * @return If we did find a path for the ball，return true，else false
+ * @param map The 2D array representing the maze (walls, paths, etc.)
+ * @param i The current x-coordinate of the ball (row index)
+ * @param j The current y-coordinate of the ball (column index)
+ * @return True if a path is found to (6,5), otherwise false
*/
- public static boolean setWay(int[][] map, int i, int j) {
- if (map[6][5] == 2) { // means the ball find its path, ending condition
+ private static boolean setWay(int[][] map, int i, int j) {
+ if (map[6][5] == 2) {
return true;
}
- if (map[i][j] == 0) { // if the ball haven't gone through this point
- // then the ball follows the move strategy : down -> right -> up -> left
- map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2
- // first。
- if (setWay(map, i + 1, j)) { // go down
+
+ // If the current position is unvisited (0), explore it
+ if (map[i][j] == 0) {
+ // Mark the current position as '2'
+ map[i][j] = 2;
+
+ // Move down
+ if (setWay(map, i + 1, j)) {
return true;
- } else if (setWay(map, i, j + 1)) { // go right
+ }
+ // Move right
+ else if (setWay(map, i, j + 1)) {
return true;
- } else if (setWay(map, i - 1, j)) { // go up
+ }
+ // Move up
+ else if (setWay(map, i - 1, j)) {
return true;
- } else if (setWay(map, i, j - 1)) { // go left
+ }
+ // Move left
+ else if (setWay(map, i, j - 1)) {
return true;
- } else {
- // means that the current point is the dead end, the ball cannot proceed, set
- // the current point to 3 and return false, the backtraking will start, it will
- // go to the previous step and check for feasible path again
- map[i][j] = 3;
- return false;
}
- } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the
- // ball cannot hit the wall, cannot go to the path that has gone though before,
- // and cannot head to deadend.
+
+ map[i][j] = 3; // Mark as dead end (3) if no direction worked
return false;
}
+ return false;
}
- // Here is another move strategy for the ball: up->right->down->left
- public static boolean setWay2(int[][] map, int i, int j) {
- if (map[6][5] == 2) { // means the ball find its path, ending condition
+ /**
+ * Attempts to find a path through the maze using an alternative movement
+ * strategy "up -> right -> down -> left".
+ *
+ * @param map The 2D array representing the maze (walls, paths, etc.)
+ * @param i The current x-coordinate of the ball (row index)
+ * @param j The current y-coordinate of the ball (column index)
+ * @return True if a path is found to (6,5), otherwise false
+ */
+ private static boolean setWay2(int[][] map, int i, int j) {
+ if (map[6][5] == 2) {
return true;
}
- if (map[i][j] == 0) { // if the ball haven't gone through this point
- // then the ball follows the move strategy : up->right->down->left
- map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2
- // first。
- if (setWay2(map, i - 1, j)) { // go up
+
+ if (map[i][j] == 0) {
+ map[i][j] = 2;
+
+ // Move up
+ if (setWay2(map, i - 1, j)) {
return true;
- } else if (setWay2(map, i, j + 1)) { // go right
+ }
+ // Move right
+ else if (setWay2(map, i, j + 1)) {
return true;
- } else if (setWay2(map, i + 1, j)) { // go down
+ }
+ // Move down
+ else if (setWay2(map, i + 1, j)) {
return true;
- } else if (setWay2(map, i, j - 1)) { // go left
+ }
+ // Move left
+ else if (setWay2(map, i, j - 1)) {
return true;
- } else {
- // means that the current point is the dead end, the ball cannot proceed, set
- // the current point to 3 and return false, the backtraking will start, it will
- // go to the previous step and check for feasible path again
- map[i][j] = 3;
- return false;
}
- } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the
- // ball cannot hit the wall, cannot go to the path that has gone though before,
- // and cannot head to deadend.
+
+ map[i][j] = 3; // Mark as dead end (3) if no direction worked
return false;
}
+ return false;
}
}
diff --git a/src/main/java/com/thealgorithms/backtracking/NQueens.java b/src/main/java/com/thealgorithms/backtracking/NQueens.java
index 632d5441c0fa..1a8e453e34cb 100644
--- a/src/main/java/com/thealgorithms/backtracking/NQueens.java
+++ b/src/main/java/com/thealgorithms/backtracking/NQueens.java
@@ -8,18 +8,18 @@
* which N queens can be placed on the board such no two queens attack each
* other. Ex. N = 6 Solution= There are 4 possible ways Arrangement: 1 ".Q....",
* "...Q..", ".....Q", "Q.....", "..Q...", "....Q."
- *
+ *
* Arrangement: 4 "....Q.", "..Q...", "Q.....", ".....Q", "...Q..", ".Q...."
*
* Solution: Brute Force approach:
*
* Generate all possible arrangement to place N queens on N*N board. Check each
* board if queens are placed safely. If it is safe, include arrangement in
- * solution set. Otherwise ignore it
+ * solution set. Otherwise, ignore it
*
* Optimized solution: This can be solved using backtracking in below steps
*
@@ -32,15 +32,14 @@
* queen is not placed safely. If there is no such way then return an empty list
* as solution
*/
-public class NQueens {
+public final class NQueens {
+ private NQueens() {
+ }
- public static void main(String[] args) {
- placeQueens(1);
- placeQueens(2);
- placeQueens(3);
- placeQueens(4);
- placeQueens(5);
- placeQueens(6);
+ public static List> getNQueensArrangements(int queens) {
+ List> arrangements = new ArrayList<>();
+ getSolution(queens, arrangements, new int[queens], 0);
+ return arrangements;
}
public static void placeQueens(final int queens) {
@@ -51,10 +50,10 @@ public static void placeQueens(final int queens) {
} else {
System.out.println("Arrangement for placing " + queens + " queens");
}
- arrangements.forEach(arrangement -> {
- arrangement.forEach(row -> System.out.println(row));
+ for (List arrangement : arrangements) {
+ arrangement.forEach(System.out::println);
System.out.println();
- });
+ }
}
/**
diff --git a/src/main/java/com/thealgorithms/backtracking/ParenthesesGenerator.java b/src/main/java/com/thealgorithms/backtracking/ParenthesesGenerator.java
new file mode 100644
index 000000000000..bf93f946ab7b
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/ParenthesesGenerator.java
@@ -0,0 +1,50 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class generates all valid combinations of parentheses for a given number of pairs using backtracking.
+ */
+public final class ParenthesesGenerator {
+ private ParenthesesGenerator() {
+ }
+
+ /**
+ * Generates all valid combinations of parentheses for a given number of pairs.
+ *
+ * @param n The number of pairs of parentheses.
+ * @return A list of strings representing valid combinations of parentheses.
+ * @throws IllegalArgumentException if n is less than 0.
+ */
+ public static List generateParentheses(final int n) {
+ if (n < 0) {
+ throw new IllegalArgumentException("The number of pairs of parentheses cannot be negative");
+ }
+ List result = new ArrayList<>();
+ generateParenthesesHelper(result, "", 0, 0, n);
+ return result;
+ }
+
+ /**
+ * Helper function for generating all valid combinations of parentheses recursively.
+ *
+ * @param result The list to store valid combinations.
+ * @param current The current combination being formed.
+ * @param open The number of open parentheses.
+ * @param close The number of closed parentheses.
+ * @param n The total number of pairs of parentheses.
+ */
+ private static void generateParenthesesHelper(List result, final String current, final int open, final int close, final int n) {
+ if (current.length() == n * 2) {
+ result.add(current);
+ return;
+ }
+ if (open < n) {
+ generateParenthesesHelper(result, current + "(", open + 1, close, n);
+ }
+ if (close < open) {
+ generateParenthesesHelper(result, current + ")", open, close + 1, n);
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/Permutation.java b/src/main/java/com/thealgorithms/backtracking/Permutation.java
index 9ad18e1e9dc2..21d26e53980f 100644
--- a/src/main/java/com/thealgorithms/backtracking/Permutation.java
+++ b/src/main/java/com/thealgorithms/backtracking/Permutation.java
@@ -5,9 +5,11 @@
/**
* Finds all permutations of given array
- * @author Alan Piao (https://github.com/cpiao3)
+ * @author Alan Piao (Git-Alan Piao)
*/
-public class Permutation {
+public final class Permutation {
+ private Permutation() {
+ }
/**
* Find all permutations of given array using backtracking
diff --git a/src/main/java/com/thealgorithms/backtracking/PowerSum.java b/src/main/java/com/thealgorithms/backtracking/PowerSum.java
index 72af17d48bd4..b34ba660ebd7 100644
--- a/src/main/java/com/thealgorithms/backtracking/PowerSum.java
+++ b/src/main/java/com/thealgorithms/backtracking/PowerSum.java
@@ -1,44 +1,51 @@
package com.thealgorithms.backtracking;
-/*
- * Problem Statement :
- * Find the number of ways that a given integer, N , can be expressed as the sum of the Xth powers
- * of unique, natural numbers. For example, if N=100 and X=3, we have to find all combinations of
- * unique cubes adding up to 100. The only solution is 1^3+2^3+3^3+4^3. Therefore output will be 1.
+/**
+ * Problem Statement:
+ * Find the number of ways that a given integer, N, can be expressed as the sum of the Xth powers
+ * of unique, natural numbers.
+ * For example, if N=100 and X=3, we have to find all combinations of unique cubes adding up to 100.
+ * The only solution is 1^3 + 2^3 + 3^3 + 4^3. Therefore, the output will be 1.
+ *
+ * N is represented by the parameter 'targetSum' in the code.
+ * X is represented by the parameter 'power' in the code.
*/
public class PowerSum {
- private int count = 0, sum = 0;
-
- public int powSum(int N, int X) {
- Sum(N, X, 1);
- return count;
+ /**
+ * Calculates the number of ways to express the target sum as a sum of Xth powers of unique natural numbers.
+ *
+ * @param targetSum The target sum to achieve (N in the problem statement)
+ * @param power The power to raise natural numbers to (X in the problem statement)
+ * @return The number of ways to express the target sum
+ */
+ public int powSum(int targetSum, int power) {
+ // Special case: when both targetSum and power are zero
+ if (targetSum == 0 && power == 0) {
+ return 1; // by convention, one way to sum to zero: use nothing
+ }
+ return sumRecursive(targetSum, power, 1, 0);
}
- // here i is the natural number which will be raised by X and added in sum.
- public void Sum(int N, int X, int i) {
- // if sum is equal to N that is one of our answer and count is increased.
- if (sum == N) {
- count++;
- return;
- } // we will be adding next natural number raised to X only if on adding it in sum the
- // result is less than N.
- else if (sum + power(i, X) <= N) {
- sum += power(i, X);
- Sum(N, X, i + 1);
- // backtracking and removing the number added last since no possible combination is
- // there with it.
- sum -= power(i, X);
+ /**
+ * Recursively calculates the number of ways to express the remaining sum as a sum of Xth powers.
+ *
+ * @param remainingSum The remaining sum to achieve
+ * @param power The power to raise natural numbers to (X in the problem statement)
+ * @param currentNumber The current natural number being considered
+ * @param currentSum The current sum of powered numbers
+ * @return The number of valid combinations
+ */
+ private int sumRecursive(int remainingSum, int power, int currentNumber, int currentSum) {
+ int newSum = currentSum + (int) Math.pow(currentNumber, power);
+
+ if (newSum == remainingSum) {
+ return 1;
}
- if (power(i, X) < N) {
- // calling the sum function with next natural number after backtracking if when it is
- // raised to X is still less than X.
- Sum(N, X, i + 1);
+ if (newSum > remainingSum) {
+ return 0;
}
- }
- // creating a separate power function so that it can be used again and again when required.
- private int power(int a, int b) {
- return (int) Math.pow(a, b);
+ return sumRecursive(remainingSum, power, currentNumber + 1, newSum) + sumRecursive(remainingSum, power, currentNumber + 1, currentSum);
}
}
diff --git a/src/main/java/com/thealgorithms/backtracking/SubsequenceFinder.java b/src/main/java/com/thealgorithms/backtracking/SubsequenceFinder.java
new file mode 100644
index 000000000000..4a159dbfe0b1
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/SubsequenceFinder.java
@@ -0,0 +1,54 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Class generates all subsequences for a given list of elements using backtracking
+ */
+public final class SubsequenceFinder {
+ private SubsequenceFinder() {
+ }
+
+ /**
+ * Find all subsequences of given list using backtracking
+ *
+ * @param sequence a list of items on the basis of which we need to generate all subsequences
+ * @param the type of elements in the array
+ * @return a list of all subsequences
+ */
+ public static List> generateAll(List sequence) {
+ List> allSubSequences = new ArrayList<>();
+ if (sequence.isEmpty()) {
+ allSubSequences.add(new ArrayList<>());
+ return allSubSequences;
+ }
+ List currentSubsequence = new ArrayList<>();
+ backtrack(sequence, currentSubsequence, 0, allSubSequences);
+ return allSubSequences;
+ }
+
+ /**
+ * Iterate through each branch of states
+ * We know that each state has exactly two branching
+ * It terminates when it reaches the end of the given sequence
+ *
+ * @param sequence all elements
+ * @param currentSubsequence current subsequence
+ * @param index current index
+ * @param allSubSequences contains all sequences
+ * @param the type of elements which we generate
+ */
+ private static void backtrack(List sequence, List currentSubsequence, final int index, List> allSubSequences) {
+ assert index <= sequence.size();
+ if (index == sequence.size()) {
+ allSubSequences.add(new ArrayList<>(currentSubsequence));
+ return;
+ }
+
+ backtrack(sequence, currentSubsequence, index + 1, allSubSequences);
+ currentSubsequence.add(sequence.get(index));
+ backtrack(sequence, currentSubsequence, index + 1, allSubSequences);
+ currentSubsequence.removeLast();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/WordPatternMatcher.java b/src/main/java/com/thealgorithms/backtracking/WordPatternMatcher.java
new file mode 100644
index 000000000000..1854cab20a7f
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/WordPatternMatcher.java
@@ -0,0 +1,86 @@
+package com.thealgorithms.backtracking;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Class to determine if a pattern matches a string using backtracking.
+ *
+ * Example:
+ * Pattern: "abab"
+ * Input String: "JavaPythonJavaPython"
+ * Output: true
+ *
+ * Pattern: "aaaa"
+ * Input String: "JavaJavaJavaJava"
+ * Output: true
+ *
+ * Pattern: "aabb"
+ * Input String: "JavaPythonPythonJava"
+ * Output: false
+ */
+public final class WordPatternMatcher {
+ private WordPatternMatcher() {
+ }
+
+ /**
+ * Determines if the given pattern matches the input string using backtracking.
+ *
+ * @param pattern The pattern to match.
+ * @param inputString The string to match against the pattern.
+ * @return True if the pattern matches the string, False otherwise.
+ */
+ public static boolean matchWordPattern(String pattern, String inputString) {
+ Map patternMap = new HashMap<>();
+ Map strMap = new HashMap<>();
+ return backtrack(pattern, inputString, 0, 0, patternMap, strMap);
+ }
+
+ /**
+ * Backtracking helper function to check if the pattern matches the string.
+ *
+ * @param pattern The pattern string.
+ * @param inputString The string to match against the pattern.
+ * @param patternIndex Current index in the pattern.
+ * @param strIndex Current index in the input string.
+ * @param patternMap Map to store pattern characters to string mappings.
+ * @param strMap Map to store string to pattern character mappings.
+ * @return True if the pattern matches, False otherwise.
+ */
+ private static boolean backtrack(String pattern, String inputString, int patternIndex, int strIndex, Map patternMap, Map strMap) {
+ if (patternIndex == pattern.length() && strIndex == inputString.length()) {
+ return true;
+ }
+ if (patternIndex == pattern.length() || strIndex == inputString.length()) {
+ return false;
+ }
+
+ char currentChar = pattern.charAt(patternIndex);
+ if (patternMap.containsKey(currentChar)) {
+ String mappedStr = patternMap.get(currentChar);
+ if (inputString.startsWith(mappedStr, strIndex)) {
+ return backtrack(pattern, inputString, patternIndex + 1, strIndex + mappedStr.length(), patternMap, strMap);
+ } else {
+ return false;
+ }
+ }
+
+ for (int end = strIndex + 1; end <= inputString.length(); end++) {
+ String substring = inputString.substring(strIndex, end);
+ if (strMap.containsKey(substring)) {
+ continue;
+ }
+
+ patternMap.put(currentChar, substring);
+ strMap.put(substring, currentChar);
+ if (backtrack(pattern, inputString, patternIndex + 1, end, patternMap, strMap)) {
+ return true;
+ }
+
+ patternMap.remove(currentChar);
+ strMap.remove(substring);
+ }
+
+ return false;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/backtracking/WordSearch.java b/src/main/java/com/thealgorithms/backtracking/WordSearch.java
index 4ab81bfd7d67..174ca90ccaab 100644
--- a/src/main/java/com/thealgorithms/backtracking/WordSearch.java
+++ b/src/main/java/com/thealgorithms/backtracking/WordSearch.java
@@ -1,35 +1,39 @@
package com.thealgorithms.backtracking;
-/*
-Word Search Problem (https://en.wikipedia.org/wiki/Word_search)
-
-Given an m x n grid of characters board and a string word, return true if word exists in the grid.
-
-The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are
-those horizontally or vertically neighboring. The same letter cell may not be used more than once.
-
-For example,
-Given board =
-
-[
- ['A','B','C','E'],
- ['S','F','C','S'],
- ['A','D','E','E']
-]
-word = "ABCCED", -> returns true,
-word = "SEE", -> returns true,
-word = "ABCB", -> returns false.
-*/
-
-/*
- Solution
- Depth First Search in matrix (as multiple sources possible) with backtracking
- like finding cycle in a directed graph. Maintain a record of path
-
- Tx = O(m * n * 3^L): for each cell, we look at 3 options (not 4 as that one will be visited), we
- do it L times Sx = O(L) : stack size is max L
-*/
-
+/**
+ * Word Search Problem
+ *
+ * This class solves the word search problem where given an m x n grid of characters (board)
+ * and a target word, the task is to check if the word exists in the grid.
+ * The word can be constructed from sequentially adjacent cells (horizontally or vertically),
+ * and the same cell may not be used more than once in constructing the word.
+ *
+ * Example:
+ * - For board =
+ * [
+ * ['A','B','C','E'],
+ * ['S','F','C','S'],
+ * ['A','D','E','E']
+ * ]
+ * and word = "ABCCED", -> returns true
+ * and word = "SEE", -> returns true
+ * and word = "ABCB", -> returns false
+ *
+ * Solution:
+ * - Depth First Search (DFS) with backtracking is used to explore possible paths from any cell
+ * matching the first letter of the word. DFS ensures that we search all valid paths, while
+ * backtracking helps in reverting decisions when a path fails to lead to a solution.
+ *
+ * Time Complexity: O(m * n * 3^L)
+ * - m = number of rows in the board
+ * - n = number of columns in the board
+ * - L = length of the word
+ * - For each cell, we look at 3 possible directions (since we exclude the previously visited direction),
+ * and we do this for L letters.
+ *
+ * Space Complexity: O(L)
+ * - Stack space for the recursive DFS function, where L is the maximum depth of recursion (length of the word).
+ */
public class WordSearch {
private final int[] dx = {0, 0, 1, -1};
private final int[] dy = {1, -1, 0, 0};
@@ -37,27 +41,55 @@ public class WordSearch {
private char[][] board;
private String word;
+ /**
+ * Checks if the given (x, y) coordinates are valid positions in the board.
+ *
+ * @param x The row index.
+ * @param y The column index.
+ * @return True if the coordinates are within the bounds of the board; false otherwise.
+ */
private boolean isValid(int x, int y) {
return x >= 0 && x < board.length && y >= 0 && y < board[0].length;
}
+ /**
+ * Performs Depth First Search (DFS) from the cell (x, y)
+ * to search for the next character in the word.
+ *
+ * @param x The current row index.
+ * @param y The current column index.
+ * @param nextIdx The index of the next character in the word to be matched.
+ * @return True if a valid path is found to match the remaining characters of the word; false otherwise.
+ */
private boolean doDFS(int x, int y, int nextIdx) {
visited[x][y] = true;
if (nextIdx == word.length()) {
return true;
}
+
for (int i = 0; i < 4; ++i) {
int xi = x + dx[i];
int yi = y + dy[i];
if (isValid(xi, yi) && board[xi][yi] == word.charAt(nextIdx) && !visited[xi][yi]) {
boolean exists = doDFS(xi, yi, nextIdx + 1);
- if (exists) return true;
+ if (exists) {
+ return true;
+ }
}
}
- visited[x][y] = false;
+
+ visited[x][y] = false; // Backtrack
return false;
}
+ /**
+ * Main function to check if the word exists in the board. It initiates DFS from any
+ * cell that matches the first character of the word.
+ *
+ * @param board The 2D grid of characters (the board).
+ * @param word The target word to search for in the board.
+ * @return True if the word exists in the board; false otherwise.
+ */
public boolean exist(char[][] board, String word) {
this.board = board;
this.word = word;
@@ -66,7 +98,9 @@ public boolean exist(char[][] board, String word) {
if (board[i][j] == word.charAt(0)) {
visited = new boolean[board.length][board[0].length];
boolean exists = doDFS(i, j, 1);
- if (exists) return true;
+ if (exists) {
+ return true;
+ }
}
}
}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java b/src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java
new file mode 100644
index 000000000000..e6bd35720d9f
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/BcdConversion.java
@@ -0,0 +1,82 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides methods to convert between BCD (Binary-Coded Decimal) and decimal numbers.
+ *
+ * BCD is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of binary digits, usually four or eight.
+ *
+ * For more information, refer to the
+ * Binary-Coded Decimal Wikipedia page.
+ *
+ * Example usage:
+ *
+ * int decimal = BcdConversion.bcdToDecimal(0x1234);
+ * System.out.println("BCD 0x1234 to decimal: " + decimal); // Output: 1234
+ *
+ * int bcd = BcdConversion.decimalToBcd(1234);
+ * System.out.println("Decimal 1234 to BCD: " + Integer.toHexString(bcd)); // Output: 0x1234
+ *
+ */
+public final class BcdConversion {
+ private BcdConversion() {
+ }
+
+ /**
+ * Converts a BCD (Binary-Coded Decimal) number to a decimal number.
+ *
Steps:
+ *
1. Validate the BCD number to ensure all digits are between 0 and 9.
+ *
2. Extract the last 4 bits (one BCD digit) from the BCD number.
+ *
3. Multiply the extracted digit by the corresponding power of 10 and add it to the decimal number.
+ *
4. Shift the BCD number right by 4 bits to process the next BCD digit.
+ *
5. Repeat steps 1-4 until the BCD number is zero.
+ *
+ * @param bcd The BCD number.
+ * @return The corresponding decimal number.
+ * @throws IllegalArgumentException if the BCD number contains invalid digits.
+ */
+ public static int bcdToDecimal(int bcd) {
+ int decimal = 0;
+ int multiplier = 1;
+
+ // Validate BCD digits
+ while (bcd > 0) {
+ int digit = bcd & 0xF;
+ if (digit > 9) {
+ throw new IllegalArgumentException("Invalid BCD digit: " + digit);
+ }
+ decimal += digit * multiplier;
+ multiplier *= 10;
+ bcd >>= 4;
+ }
+ return decimal;
+ }
+
+ /**
+ * Converts a decimal number to BCD (Binary-Coded Decimal).
+ *
Steps:
+ *
1. Check if the decimal number is within the valid range for BCD (0 to 9999).
+ *
2. Extract the last decimal digit from the decimal number.
+ *
3. Shift the digit to the correct BCD position and add it to the BCD number.
+ *
4. Remove the last decimal digit from the decimal number.
+ *
5. Repeat steps 2-4 until the decimal number is zero.
+ *
+ * @param decimal The decimal number.
+ * @return The corresponding BCD number.
+ * @throws IllegalArgumentException if the decimal number is greater than 9999.
+ */
+ public static int decimalToBcd(int decimal) {
+ if (decimal < 0 || decimal > 9999) {
+ throw new IllegalArgumentException("Value out of bounds for BCD representation: " + decimal);
+ }
+
+ int bcd = 0;
+ int shift = 0;
+ while (decimal > 0) {
+ int digit = decimal % 10;
+ bcd |= (digit << (shift * 4));
+ decimal /= 10;
+ shift++;
+ }
+ return bcd;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/BinaryPalindromeCheck.java b/src/main/java/com/thealgorithms/bitmanipulation/BinaryPalindromeCheck.java
new file mode 100644
index 000000000000..0d6fd140c720
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/BinaryPalindromeCheck.java
@@ -0,0 +1,43 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class contains a method to check if the binary representation of a number is a palindrome.
+ *
+ * A binary palindrome is a number whose binary representation is the same when read from left to right and right to left.
+ * For example, the number 9 has a binary representation of 1001, which is a palindrome.
+ * The number 10 has a binary representation of 1010, which is not a palindrome.
+ *
+ *
+ * @author Hardvan
+ */
+public final class BinaryPalindromeCheck {
+ private BinaryPalindromeCheck() {
+ }
+
+ /**
+ * Checks if the binary representation of a number is a palindrome.
+ *
+ * @param x The number to check.
+ * @return True if the binary representation is a palindrome, otherwise false.
+ */
+ public static boolean isBinaryPalindrome(int x) {
+ int reversed = reverseBits(x);
+ return x == reversed;
+ }
+
+ /**
+ * Helper function to reverse all the bits of an integer.
+ *
+ * @param x The number to reverse the bits of.
+ * @return The number with reversed bits.
+ */
+ private static int reverseBits(int x) {
+ int result = 0;
+ while (x > 0) {
+ result <<= 1;
+ result |= (x & 1);
+ x >>= 1;
+ }
+ return result;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/BitSwap.java b/src/main/java/com/thealgorithms/bitmanipulation/BitSwap.java
new file mode 100644
index 000000000000..40b3097b1276
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/BitSwap.java
@@ -0,0 +1,15 @@
+package com.thealgorithms.bitmanipulation;
+
+public final class BitSwap {
+ private BitSwap() {
+ }
+ /*
+ * @brief Swaps the bits at the position posA and posB from data
+ */
+ public static int bitSwap(int data, final int posA, final int posB) {
+ if (SingleBitOperations.getBit(data, posA) != SingleBitOperations.getBit(data, posB)) {
+ data ^= (1 << posA) ^ (1 << posB);
+ }
+ return data;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/BooleanAlgebraGates.java b/src/main/java/com/thealgorithms/bitmanipulation/BooleanAlgebraGates.java
new file mode 100644
index 000000000000..869466320831
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/BooleanAlgebraGates.java
@@ -0,0 +1,111 @@
+package com.thealgorithms.bitmanipulation;
+
+import java.util.List;
+
+/**
+ * Implements various Boolean algebra gates (AND, OR, NOT, XOR, NAND, NOR)
+ */
+public final class BooleanAlgebraGates {
+
+ private BooleanAlgebraGates() {
+ // Prevent instantiation
+ }
+
+ /**
+ * Represents a Boolean gate that takes multiple inputs and returns a result.
+ */
+ interface BooleanGate {
+ /**
+ * Evaluates the gate with the given inputs.
+ *
+ * @param inputs The input values for the gate.
+ * @return The result of the evaluation.
+ */
+ boolean evaluate(List inputs);
+ }
+
+ /**
+ * AND Gate implementation.
+ * Returns true if all inputs are true; otherwise, false.
+ */
+ static class ANDGate implements BooleanGate {
+ @Override
+ public boolean evaluate(List inputs) {
+ for (boolean input : inputs) {
+ if (!input) {
+ return false;
+ }
+ }
+ return true;
+ }
+ }
+
+ /**
+ * OR Gate implementation.
+ * Returns true if at least one input is true; otherwise, false.
+ */
+ static class ORGate implements BooleanGate {
+ @Override
+ public boolean evaluate(List inputs) {
+ for (boolean input : inputs) {
+ if (input) {
+ return true;
+ }
+ }
+ return false;
+ }
+ }
+
+ /**
+ * NOT Gate implementation (Unary operation).
+ * Negates a single input value.
+ */
+ static class NOTGate {
+ /**
+ * Evaluates the negation of the input.
+ *
+ * @param input The input value to be negated.
+ * @return The negated value.
+ */
+ public boolean evaluate(boolean input) {
+ return !input;
+ }
+ }
+
+ /**
+ * XOR Gate implementation.
+ * Returns true if an odd number of inputs are true; otherwise, false.
+ */
+ static class XORGate implements BooleanGate {
+ @Override
+ public boolean evaluate(List inputs) {
+ boolean result = false;
+ for (boolean input : inputs) {
+ result ^= input;
+ }
+ return result;
+ }
+ }
+
+ /**
+ * NAND Gate implementation.
+ * Returns true if at least one input is false; otherwise, false.
+ */
+ static class NANDGate implements BooleanGate {
+ @Override
+ public boolean evaluate(List inputs) {
+ return !new ANDGate().evaluate(inputs); // Equivalent to negation of AND
+ }
+ }
+
+ /**
+ * NOR Gate implementation.
+ * Returns true if all inputs are false; otherwise, false.
+ */
+ static class NORGate implements BooleanGate {
+ @Override
+ public boolean evaluate(List inputs) {
+ return !new ORGate().evaluate(inputs); // Equivalent to negation of OR
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/ClearLeftmostSetBit.java b/src/main/java/com/thealgorithms/bitmanipulation/ClearLeftmostSetBit.java
new file mode 100644
index 000000000000..3e9a4a21183f
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/ClearLeftmostSetBit.java
@@ -0,0 +1,39 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * ClearLeftmostSetBit class contains a method to clear the leftmost set bit of a number.
+ * The leftmost set bit is the leftmost bit that is set to 1 in the binary representation of a number.
+ *
+ * Example:
+ * 26 (11010) -> 10 (01010)
+ * 1 (1) -> 0 (0)
+ * 7 (111) -> 3 (011)
+ * 6 (0110) -> 2 (0010)
+ *
+ * @author Hardvan
+ */
+public final class ClearLeftmostSetBit {
+ private ClearLeftmostSetBit() {
+ }
+
+ /**
+ * Clears the leftmost set bit (1) of a given number.
+ * Step 1: Find the position of the leftmost set bit
+ * Step 2: Create a mask with all bits set except for the leftmost set bit
+ * Step 3: Clear the leftmost set bit using AND with the mask
+ *
+ * @param num The input number.
+ * @return The number after clearing the leftmost set bit.
+ */
+ public static int clearLeftmostSetBit(int num) {
+ int pos = 0;
+ int temp = num;
+ while (temp > 0) {
+ temp >>= 1;
+ pos++;
+ }
+
+ int mask = ~(1 << (pos - 1));
+ return num & mask;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/CountLeadingZeros.java b/src/main/java/com/thealgorithms/bitmanipulation/CountLeadingZeros.java
new file mode 100644
index 000000000000..318334f0b951
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/CountLeadingZeros.java
@@ -0,0 +1,39 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * CountLeadingZeros class contains a method to count the number of leading zeros in the binary representation of a number.
+ * The number of leading zeros is the number of zeros before the leftmost 1 bit.
+ * For example, the number 5 has 29 leading zeros in its 32-bit binary representation.
+ * The number 0 has 32 leading zeros.
+ * The number 1 has 31 leading zeros.
+ * The number -1 has no leading zeros.
+ *
+ * @author Hardvan
+ */
+public final class CountLeadingZeros {
+ private CountLeadingZeros() {
+ }
+
+ /**
+ * Counts the number of leading zeros in the binary representation of a number.
+ * Method: Keep shifting the mask to the right until the leftmost bit is 1.
+ * The number of shifts is the number of leading zeros.
+ *
+ * @param num The input number.
+ * @return The number of leading zeros.
+ */
+ public static int countLeadingZeros(int num) {
+ if (num == 0) {
+ return 32;
+ }
+
+ int count = 0;
+ int mask = 1 << 31;
+ while ((mask & num) == 0) {
+ count++;
+ mask >>>= 1;
+ }
+
+ return count;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/others/countSetBits.java b/src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.java
similarity index 61%
rename from src/main/java/com/thealgorithms/others/countSetBits.java
rename to src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.java
index 04e0d6f62e6e..242f35fc35f2 100644
--- a/src/main/java/com/thealgorithms/others/countSetBits.java
+++ b/src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.java
@@ -1,6 +1,6 @@
-package com.thealgorithms.others;
+package com.thealgorithms.bitmanipulation;
-public class countSetBits {
+public class CountSetBits {
/**
* The below algorithm is called as Brian Kernighan's algorithm
@@ -40,7 +40,7 @@ public class countSetBits {
* @param num takes Long number whose number of set bit is to be found
* @return the count of set bits in the binary equivalent
*/
- public long countsetBits(long num) {
+ public long countSetBits(long num) {
long cnt = 0;
while (num > 0) {
cnt++;
@@ -48,4 +48,32 @@ public long countsetBits(long num) {
}
return cnt;
}
+
+ /**
+ * This approach takes O(1) running time to count the set bits, but requires a pre-processing.
+ *
+ * So, we divide our 32-bit input into 8-bit chunks, with four chunks. We have 8 bits in each chunk.
+ *
+ * Then the range is from 0-255 (0 to 2^7).
+ * So, we may need to count set bits from 0 to 255 in individual chunks.
+ *
+ * @param num takes a long number
+ * @return the count of set bits in the binary equivalent
+ */
+ public int lookupApproach(int num) {
+ int[] table = new int[256];
+ table[0] = 0;
+
+ for (int i = 1; i < 256; i++) {
+ table[i] = (i & 1) + table[i >> 1]; // i >> 1 equals to i/2
+ }
+
+ int res = 0;
+ for (int i = 0; i < 4; i++) {
+ res += table[num & 0xff];
+ num >>= 8;
+ }
+
+ return res;
+ }
}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/FindNthBit.java b/src/main/java/com/thealgorithms/bitmanipulation/FindNthBit.java
new file mode 100644
index 000000000000..7a35fc3feebf
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/FindNthBit.java
@@ -0,0 +1,46 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * A utility class to find the Nth bit of a given number.
+ *
+ *
This class provides a method to extract the value of the Nth bit (either 0 or 1)
+ * from the binary representation of a given integer.
+ *
+ *
Example:
+ *
{@code
+ * int result = FindNthBit.findNthBit(5, 2); // returns 0 as the 2nd bit of 5 (binary 101) is 0.
+ * }
+ *
+ *
Author: Tuhinm2002
+ */
+public final class FindNthBit {
+
+ /**
+ * Private constructor to prevent instantiation.
+ *
+ *
This is a utility class, and it should not be instantiated.
+ * Attempting to instantiate this class will throw an UnsupportedOperationException.
+ */
+ private FindNthBit() {
+ throw new UnsupportedOperationException("Utility class");
+ }
+
+ /**
+ * Finds the value of the Nth bit of the given number.
+ *
+ *
This method uses bitwise operations to extract the Nth bit from the
+ * binary representation of the given integer.
+ *
+ * @param num the integer number whose Nth bit is to be found
+ * @param n the bit position (1-based) to retrieve
+ * @return the value of the Nth bit (0 or 1)
+ * @throws IllegalArgumentException if the bit position is less than 1
+ */
+ public static int findNthBit(int num, int n) {
+ if (n < 1) {
+ throw new IllegalArgumentException("Bit position must be greater than or equal to 1.");
+ }
+ // Shifting the number to the right by (n - 1) positions and checking the last bit
+ return (num & (1 << (n - 1))) >> (n - 1);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/FirstDifferentBit.java b/src/main/java/com/thealgorithms/bitmanipulation/FirstDifferentBit.java
new file mode 100644
index 000000000000..9a761c572e2c
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/FirstDifferentBit.java
@@ -0,0 +1,33 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to find the first differing bit
+ * between two integers.
+ *
+ * Example:
+ * x = 10 (1010 in binary)
+ * y = 12 (1100 in binary)
+ * The first differing bit is at index 1 (0-based)
+ * So, the output will be 1
+ *
+ * @author Hardvan
+ */
+public final class FirstDifferentBit {
+ private FirstDifferentBit() {
+ }
+
+ /**
+ * Identifies the index of the first differing bit between two integers.
+ * Steps:
+ * 1. XOR the two integers to get the differing bits
+ * 2. Find the index of the first set bit in XOR result
+ *
+ * @param x the first integer
+ * @param y the second integer
+ * @return the index of the first differing bit (0-based)
+ */
+ public static int firstDifferentBit(int x, int y) {
+ int diff = x ^ y;
+ return Integer.numberOfTrailingZeros(diff);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/GenerateSubsets.java b/src/main/java/com/thealgorithms/bitmanipulation/GenerateSubsets.java
new file mode 100644
index 000000000000..f1b812495c1b
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/GenerateSubsets.java
@@ -0,0 +1,44 @@
+package com.thealgorithms.bitmanipulation;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class provides a method to generate all subsets (power set)
+ * of a given set using bit manipulation.
+ *
+ * @author Hardvan
+ */
+public final class GenerateSubsets {
+ private GenerateSubsets() {
+ }
+
+ /**
+ * Generates all subsets of a given set using bit manipulation.
+ * Steps:
+ * 1. Iterate over all numbers from 0 to 2^n - 1.
+ * 2. For each number, iterate over all bits from 0 to n - 1.
+ * 3. If the i-th bit of the number is set, add the i-th element of the set to the current subset.
+ * 4. Add the current subset to the list of subsets.
+ * 5. Return the list of subsets.
+ *
+ * @param set the input set of integers
+ * @return a list of all subsets represented as lists of integers
+ */
+ public static List> generateSubsets(int[] set) {
+ int n = set.length;
+ List> subsets = new ArrayList<>();
+
+ for (int mask = 0; mask < (1 << n); mask++) {
+ List subset = new ArrayList<>();
+ for (int i = 0; i < n; i++) {
+ if ((mask & (1 << i)) != 0) {
+ subset.add(set[i]);
+ }
+ }
+ subsets.add(subset);
+ }
+
+ return subsets;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/GrayCodeConversion.java b/src/main/java/com/thealgorithms/bitmanipulation/GrayCodeConversion.java
new file mode 100644
index 000000000000..83cd30c7d50a
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/GrayCodeConversion.java
@@ -0,0 +1,44 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Gray code is a binary numeral system where two successive values differ in only one bit.
+ * This is a simple conversion between binary and Gray code.
+ * Example:
+ * 7 -> 0111 -> 0100 -> 4
+ * 4 -> 0100 -> 0111 -> 7
+ * 0 -> 0000 -> 0000 -> 0
+ * 1 -> 0001 -> 0000 -> 0
+ * 2 -> 0010 -> 0011 -> 3
+ * 3 -> 0011 -> 0010 -> 2
+ *
+ * @author Hardvan
+ */
+public final class GrayCodeConversion {
+ private GrayCodeConversion() {
+ }
+
+ /**
+ * Converts a binary number to Gray code.
+ *
+ * @param num The binary number.
+ * @return The corresponding Gray code.
+ */
+ public static int binaryToGray(int num) {
+ return num ^ (num >> 1);
+ }
+
+ /**
+ * Converts a Gray code number back to binary.
+ *
+ * @param gray The Gray code number.
+ * @return The corresponding binary number.
+ */
+ public static int grayToBinary(int gray) {
+ int binary = gray;
+ while (gray > 0) {
+ gray >>= 1;
+ binary ^= gray;
+ }
+ return binary;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/HammingDistance.java b/src/main/java/com/thealgorithms/bitmanipulation/HammingDistance.java
new file mode 100644
index 000000000000..4c24909ef234
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/HammingDistance.java
@@ -0,0 +1,29 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * The Hamming distance between two integers is the number of positions at which the corresponding bits are different.
+ * Given two integers x and y, calculate the Hamming distance.
+ * Example:
+ * Input: x = 1, y = 4
+ * Output: 2
+ * Explanation: 1 (0001) and 4 (0100) have 2 differing bits.
+ *
+ * @author Hardvan
+ */
+public final class HammingDistance {
+ private HammingDistance() {
+ }
+
+ /**
+ * Calculates the Hamming distance between two integers.
+ * The Hamming distance is the number of differing bits between the two integers.
+ *
+ * @param x The first integer.
+ * @param y The second integer.
+ * @return The Hamming distance (number of differing bits).
+ */
+ public static int hammingDistance(int x, int y) {
+ int xor = x ^ y;
+ return Integer.bitCount(xor);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/HigherLowerPowerOfTwo.java b/src/main/java/com/thealgorithms/bitmanipulation/HigherLowerPowerOfTwo.java
new file mode 100644
index 000000000000..0fb058b2b8a3
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/HigherLowerPowerOfTwo.java
@@ -0,0 +1,54 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * HigherLowerPowerOfTwo class has two methods to find the next higher and lower power of two.
+ *
+ * nextHigherPowerOfTwo method finds the next higher power of two.
+ * nextLowerPowerOfTwo method finds the next lower power of two.
+ * Both methods take an integer as input and return the next higher or lower power of two.
+ * If the input is less than 1, the next higher power of two is 1.
+ * If the input is less than or equal to 1, the next lower power of two is 0.
+ * nextHigherPowerOfTwo method uses bitwise operations to find the next higher power of two.
+ * nextLowerPowerOfTwo method uses Integer.highestOneBit method to find the next lower power of two.
+ * The time complexity of both methods is O(1).
+ * The space complexity of both methods is O(1).
+ *
+ *
+ * @author Hardvan
+ */
+public final class HigherLowerPowerOfTwo {
+ private HigherLowerPowerOfTwo() {
+ }
+
+ /**
+ * Finds the next higher power of two.
+ *
+ * @param x The given number.
+ * @return The next higher power of two.
+ */
+ public static int nextHigherPowerOfTwo(int x) {
+ if (x < 1) {
+ return 1;
+ }
+ x--;
+ x |= x >> 1;
+ x |= x >> 2;
+ x |= x >> 4;
+ x |= x >> 8;
+ x |= x >> 16;
+ return x + 1;
+ }
+
+ /**
+ * Finds the next lower power of two.
+ *
+ * @param x The given number.
+ * @return The next lower power of two.
+ */
+ public static int nextLowerPowerOfTwo(int x) {
+ if (x < 1) {
+ return 0;
+ }
+ return Integer.highestOneBit(x);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/HighestSetBit.java b/src/main/java/com/thealgorithms/bitmanipulation/HighestSetBit.java
new file mode 100644
index 000000000000..2398b8214371
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/HighestSetBit.java
@@ -0,0 +1,54 @@
+package com.thealgorithms.bitmanipulation;
+
+import java.util.Optional;
+
+/**
+ * Find Highest Set Bit
+ *
+ * This class provides a utility method to calculate the position of the highest
+ * (most significant) bit that is set to 1 in a given non-negative integer.
+ * It is often used in bit manipulation tasks to find the left-most set bit in binary
+ * representation of a number.
+ *
+ * Example:
+ * - For input 18 (binary 10010), the highest set bit is at position 4 (zero-based index).
+ *
+ * @author Bama Charan Chhandogi
+ * @version 1.0
+ * @since 2021-06-23
+ */
+public final class HighestSetBit {
+
+ private HighestSetBit() {
+ }
+
+ /**
+ * Finds the highest (most significant) set bit in the given integer.
+ * The method returns the position (index) of the highest set bit as an {@link Optional}.
+ *
+ * - If the number is 0, no bits are set, and the method returns {@link Optional#empty()}.
+ * - If the number is negative, the method throws {@link IllegalArgumentException}.
+ *
+ * @param num The input integer for which the highest set bit is to be found. It must be non-negative.
+ * @return An {@link Optional} containing the index of the highest set bit (zero-based).
+ * Returns {@link Optional#empty()} if the number is 0.
+ * @throws IllegalArgumentException if the input number is negative.
+ */
+ public static Optional findHighestSetBit(int num) {
+ if (num < 0) {
+ throw new IllegalArgumentException("Input cannot be negative");
+ }
+
+ if (num == 0) {
+ return Optional.empty();
+ }
+
+ int position = 0;
+ while (num > 0) {
+ num >>= 1;
+ position++;
+ }
+
+ return Optional.of(position - 1); // Subtract 1 to convert to zero-based index
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/IndexOfRightMostSetBit.java b/src/main/java/com/thealgorithms/bitmanipulation/IndexOfRightMostSetBit.java
new file mode 100644
index 000000000000..1b8962344ea7
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/IndexOfRightMostSetBit.java
@@ -0,0 +1,44 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Utility class for bit manipulation operations.
+ * This class provides methods to work with bitwise operations.
+ * Specifically, it includes a method to find the index of the rightmost set bit
+ * in an integer.
+ * This class is not meant to be instantiated.
+ *
+ * Author: Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+public final class IndexOfRightMostSetBit {
+
+ private IndexOfRightMostSetBit() {
+ }
+
+ /**
+ * Finds the index of the rightmost set bit in the given integer.
+ * The index is zero-based, meaning the rightmost bit has an index of 0.
+ *
+ * @param n the integer to check for the rightmost set bit
+ * @return the index of the rightmost set bit; -1 if there are no set bits
+ * (i.e., the input integer is 0)
+ */
+ public static int indexOfRightMostSetBit(int n) {
+ if (n == 0) {
+ return -1; // No set bits
+ }
+
+ // Handle negative numbers by finding the two's complement
+ if (n < 0) {
+ n = -n;
+ n = n & (~n + 1); // Isolate the rightmost set bit
+ }
+
+ int index = 0;
+ while ((n & 1) == 0) {
+ n = n >> 1;
+ index++;
+ }
+
+ return index;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/IsEven.java b/src/main/java/com/thealgorithms/bitmanipulation/IsEven.java
new file mode 100644
index 000000000000..09d5383322ff
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/IsEven.java
@@ -0,0 +1,14 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Checks whether a number is even
+ * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+
+public final class IsEven {
+ private IsEven() {
+ }
+ public static boolean isEven(int number) {
+ return (number & 1) == 0;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/IsPowerTwo.java b/src/main/java/com/thealgorithms/bitmanipulation/IsPowerTwo.java
new file mode 100644
index 000000000000..4cdf3c6faa3e
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/IsPowerTwo.java
@@ -0,0 +1,32 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Utility class for checking if a number is a power of two.
+ * A power of two is a number that can be expressed as 2^n where n is a non-negative integer.
+ * This class provides a method to determine if a given integer is a power of two using bit manipulation.
+ *
+ * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+public final class IsPowerTwo {
+ private IsPowerTwo() {
+ }
+
+ /**
+ * Checks if the given integer is a power of two.
+ *
+ * A number is considered a power of two if it is greater than zero and
+ * has exactly one '1' bit in its binary representation. This method
+ * uses the property that for any power of two (n), the expression
+ * (n & (n - 1)) will be zero.
+ *
+ * @param number the integer to check
+ * @return true if the number is a power of two, false otherwise
+ */
+ public static boolean isPowerTwo(int number) {
+ if (number <= 0) {
+ return false;
+ }
+ int ans = number & (number - 1);
+ return ans == 0;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/LowestSetBit.java b/src/main/java/com/thealgorithms/bitmanipulation/LowestSetBit.java
new file mode 100644
index 000000000000..127b6fa2c0b1
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/LowestSetBit.java
@@ -0,0 +1,34 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Lowest Set Bit
+ * @author Prayas Kumar (https://github.com/prayas7102)
+ */
+
+public final class LowestSetBit {
+ // Private constructor to hide the default public one
+ private LowestSetBit() {
+ }
+ /**
+ * Isolates the lowest set bit of the given number. For example, if n = 18
+ * (binary: 10010), the result will be 2 (binary: 00010).
+ *
+ * @param n the number whose lowest set bit will be isolated
+ * @return the isolated lowest set bit of n
+ */
+ public static int isolateLowestSetBit(int n) {
+ // Isolate the lowest set bit using n & -n
+ return n & -n;
+ }
+ /**
+ * Clears the lowest set bit of the given number.
+ * For example, if n = 18 (binary: 10010), the result will be 16 (binary: 10000).
+ *
+ * @param n the number whose lowest set bit will be cleared
+ * @return the number after clearing its lowest set bit
+ */
+ public static int clearLowestSetBit(int n) {
+ // Clear the lowest set bit using n & (n - 1)
+ return n & (n - 1);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/ModuloPowerOfTwo.java b/src/main/java/com/thealgorithms/bitmanipulation/ModuloPowerOfTwo.java
new file mode 100644
index 000000000000..537a046f77e4
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/ModuloPowerOfTwo.java
@@ -0,0 +1,28 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to compute the remainder
+ * of a number when divided by a power of two (2^n)
+ * without using division or modulo operations.
+ *
+ * @author Hardvan
+ */
+public final class ModuloPowerOfTwo {
+ private ModuloPowerOfTwo() {
+ }
+
+ /**
+ * Computes the remainder of a given integer when divided by 2^n.
+ *
+ * @param x the input number
+ * @param n the exponent (power of two)
+ * @return the remainder of x divided by 2^n
+ */
+ public static int moduloPowerOfTwo(int x, int n) {
+ if (n <= 0) {
+ throw new IllegalArgumentException("The exponent must be positive");
+ }
+
+ return x & ((1 << n) - 1);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/NextHigherSameBitCount.java b/src/main/java/com/thealgorithms/bitmanipulation/NextHigherSameBitCount.java
new file mode 100644
index 000000000000..6a764d806279
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/NextHigherSameBitCount.java
@@ -0,0 +1,30 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to find the next higher number
+ * with the same number of set bits as the given number.
+ *
+ * @author Hardvan
+ */
+public final class NextHigherSameBitCount {
+ private NextHigherSameBitCount() {
+ }
+
+ /**
+ * Finds the next higher integer with the same number of set bits.
+ * Steps:
+ * 1. Find {@code c}, the rightmost set bit of {@code n}.
+ * 2. Find {@code r}, the rightmost set bit of {@code n + c}.
+ * 3. Swap the bits of {@code r} and {@code n} to the right of {@code c}.
+ * 4. Shift the bits of {@code r} and {@code n} to the right of {@code c} to the rightmost.
+ * 5. Combine the results of steps 3 and 4.
+ *
+ * @param n the input number
+ * @return the next higher integer with the same set bit count
+ */
+ public static int nextHigherSameBitCount(int n) {
+ int c = n & -n;
+ int r = n + c;
+ return (((r ^ n) >> 2) / c) | r;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/NonRepeatingNumberFinder.java b/src/main/java/com/thealgorithms/bitmanipulation/NonRepeatingNumberFinder.java
new file mode 100644
index 000000000000..17e1a73ec062
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/NonRepeatingNumberFinder.java
@@ -0,0 +1,35 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * A utility class to find the non-repeating number in an array where every other number repeats.
+ * This class contains a method to identify the single unique number using bit manipulation.
+ *
+ * The solution leverages the properties of the XOR operation, which states that:
+ * - x ^ x = 0 for any integer x (a number XORed with itself is zero)
+ * - x ^ 0 = x for any integer x (a number XORed with zero is the number itself)
+ *
+ * Using these properties, we can find the non-repeating number in linear time with constant space.
+ *
+ * Example:
+ * Given the input array [2, 3, 5, 2, 3], the output will be 5 since it does not repeat.
+ *
+ * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ */
+public final class NonRepeatingNumberFinder {
+ private NonRepeatingNumberFinder() {
+ }
+
+ /**
+ * Finds the non-repeating number in the given array.
+ *
+ * @param arr an array of integers where every number except one appears twice
+ * @return the integer that appears only once in the array or 0 if the array is empty
+ */
+ public static int findNonRepeatingNumber(int[] arr) {
+ int result = 0;
+ for (int num : arr) {
+ result ^= num;
+ }
+ return result;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/NumberAppearingOddTimes.java b/src/main/java/com/thealgorithms/bitmanipulation/NumberAppearingOddTimes.java
new file mode 100644
index 000000000000..bd4868d4dbd5
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/NumberAppearingOddTimes.java
@@ -0,0 +1,41 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to find the element that appears an
+ * odd number of times in an array. All other elements in the array
+ * must appear an even number of times for the logic to work.
+ *
+ * The solution uses the XOR operation, which has the following properties:
+ * - a ^ a = 0 (XOR-ing the same numbers cancels them out)
+ * - a ^ 0 = a
+ * - XOR is commutative and associative.
+ *
+ * Time Complexity: O(n), where n is the size of the array.
+ * Space Complexity: O(1), as no extra space is used.
+ *
+ * Usage Example:
+ * int result = NumberAppearingOddTimes.findOddOccurrence(new int[]{1, 2, 1, 2, 3});
+ * // result will be 3
+ *
+ * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ */
+
+public final class NumberAppearingOddTimes {
+ private NumberAppearingOddTimes() {
+ }
+
+ /**
+ * Finds the element in the array that appears an odd number of times.
+ *
+ * @param arr the input array containing integers, where all elements
+ * except one appear an even number of times.
+ * @return the integer that appears an odd number of times.
+ */
+ public static int findOddOccurrence(int[] arr) {
+ int result = 0;
+ for (int num : arr) {
+ result ^= num;
+ }
+ return result;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/NumbersDifferentSigns.java b/src/main/java/com/thealgorithms/bitmanipulation/NumbersDifferentSigns.java
new file mode 100644
index 000000000000..a2da37aa81ee
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/NumbersDifferentSigns.java
@@ -0,0 +1,30 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to determine whether two integers have
+ * different signs. It utilizes the XOR operation on the two numbers:
+ *
+ * - If two numbers have different signs, their most significant bits
+ * (sign bits) will differ, resulting in a negative XOR result.
+ * - If two numbers have the same sign, the XOR result will be non-negative.
+ *
+ * Time Complexity: O(1) - Constant time operation.
+ * Space Complexity: O(1) - No extra space used.
+ *
+ * @author Bama Charan Chhandogi
+ */
+public final class NumbersDifferentSigns {
+ private NumbersDifferentSigns() {
+ }
+
+ /**
+ * Determines if two integers have different signs using bitwise XOR.
+ *
+ * @param num1 the first integer
+ * @param num2 the second integer
+ * @return true if the two numbers have different signs, false otherwise
+ */
+ public static boolean differentSigns(int num1, int num2) {
+ return (num1 ^ num2) < 0;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/OneBitDifference.java b/src/main/java/com/thealgorithms/bitmanipulation/OneBitDifference.java
new file mode 100644
index 000000000000..afec0188e299
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/OneBitDifference.java
@@ -0,0 +1,32 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to detect if two integers
+ * differ by exactly one bit flip.
+ *
+ * Example:
+ * 1 (0001) and 2 (0010) differ by exactly one bit flip.
+ * 7 (0111) and 3 (0011) differ by exactly one bit flip.
+ *
+ * @author Hardvan
+ */
+public final class OneBitDifference {
+ private OneBitDifference() {
+ }
+
+ /**
+ * Checks if two integers differ by exactly one bit.
+ *
+ * @param x the first integer
+ * @param y the second integer
+ * @return true if x and y differ by exactly one bit, false otherwise
+ */
+ public static boolean differByOneBit(int x, int y) {
+ if (x == y) {
+ return false;
+ }
+
+ int xor = x ^ y;
+ return (xor & (xor - 1)) == 0;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/OnesComplement.java b/src/main/java/com/thealgorithms/bitmanipulation/OnesComplement.java
new file mode 100644
index 000000000000..c5c068422113
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/OnesComplement.java
@@ -0,0 +1,28 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * @author - https://github.com/Monk-AbhinayVerma
+ * @Wikipedia - https://en.wikipedia.org/wiki/Ones%27_complement
+ * The class OnesComplement computes the complement of binary number
+ * and returns
+ * the complemented binary string.
+ * @return the complimented binary string
+ */
+public final class OnesComplement {
+ private OnesComplement() {
+ }
+
+ // Function to get the 1's complement of a binary number
+ public static String onesComplement(String binary) {
+ StringBuilder complement = new StringBuilder();
+ // Invert each bit to get the 1's complement
+ for (int i = 0; i < binary.length(); i++) {
+ if (binary.charAt(i) == '0') {
+ complement.append('1');
+ } else {
+ complement.append('0');
+ }
+ }
+ return complement.toString();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/ParityCheck.java b/src/main/java/com/thealgorithms/bitmanipulation/ParityCheck.java
new file mode 100644
index 000000000000..5acab4d4a362
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/ParityCheck.java
@@ -0,0 +1,34 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * The ParityCheck class provides a method to check the parity of a given number.
+ *
+ * Parity is a mathematical term that describes the property of an integer's binary representation.
+ * The parity of a binary number is the number of 1s in its binary representation.
+ * If the number of 1s is even, the parity is even; otherwise, it is odd.
+ *
+ * For example, the binary representation of 5 is 101, which has two 1s, so the parity of 5 is even.
+ * The binary representation of 6 is 110, which has two 1s, so the parity of 6 is even.
+ * The binary representation of 7 is 111, which has three 1s, so the parity of 7 is odd.
+ *
+ * @author Hardvan
+ */
+public final class ParityCheck {
+ private ParityCheck() {
+ }
+
+ /**
+ * This method checks the parity of the given number.
+ *
+ * @param n the number to check the parity of
+ * @return true if the number has even parity, false otherwise
+ */
+ public static boolean checkParity(int n) {
+ int count = 0;
+ while (n > 0) {
+ count += n & 1;
+ n >>= 1;
+ }
+ return count % 2 == 0;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/ReverseBits.java b/src/main/java/com/thealgorithms/bitmanipulation/ReverseBits.java
new file mode 100644
index 000000000000..12c269d9be48
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/ReverseBits.java
@@ -0,0 +1,41 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to reverse the bits of a 32-bit integer.
+ * Reversing the bits means that the least significant bit (LSB) becomes
+ * the most significant bit (MSB) and vice versa.
+ *
+ * Example:
+ * Input (binary): 00000010100101000001111010011100 (43261596)
+ * Output (binary): 00111001011110000010100101000000 (964176192)
+ *
+ * Time Complexity: O(32) - A fixed number of 32 iterations
+ * Space Complexity: O(1) - No extra space used
+ *
+ * Note:
+ * - If the input is negative, Java handles it using two’s complement representation.
+ * - This function works on 32-bit integers by default.
+ *
+ * @author Bama Charan Chhandogi
+ */
+public final class ReverseBits {
+ private ReverseBits() {
+ }
+
+ /**
+ * Reverses the bits of a 32-bit integer.
+ *
+ * @param n the integer whose bits are to be reversed
+ * @return the integer obtained by reversing the bits of the input
+ */
+ public static int reverseBits(int n) {
+ int result = 0;
+ int bitCount = 32;
+ for (int i = 0; i < bitCount; i++) {
+ result <<= 1; // Left shift the result to make space for the next bit
+ result |= (n & 1); // OR operation to set the least significant bit of result with the current bit of n
+ n >>= 1; // Right shift n to move on to the next bit
+ }
+ return result;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/SingleBitOperations.java b/src/main/java/com/thealgorithms/bitmanipulation/SingleBitOperations.java
new file mode 100644
index 000000000000..624a4e2b858a
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/SingleBitOperations.java
@@ -0,0 +1,68 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * A utility class for performing single-bit operations on integers.
+ * These operations include flipping, setting, clearing, and getting
+ * individual bits at specified positions.
+ *
+ * Bit positions are zero-indexed (i.e., the least significant bit is at position 0).
+ * These methods leverage bitwise operations for optimal performance.
+ *
+ * Examples:
+ * - `flipBit(3, 1)` flips the bit at index 1 in binary `11` (result: `1`).
+ * - `setBit(4, 0)` sets the bit at index 0 in `100` (result: `101` or 5).
+ * - `clearBit(7, 1)` clears the bit at index 1 in `111` (result: `101` or 5).
+ * - `getBit(6, 0)` checks if the least significant bit is set (result: `0`).
+ *
+ * Time Complexity: O(1) for all operations.
+ *
+ * Author: lukasb1b (https://github.com/lukasb1b)
+ */
+public final class SingleBitOperations {
+ private SingleBitOperations() {
+ }
+
+ /**
+ * Flips (toggles) the bit at the specified position.
+ *
+ * @param num the input number
+ * @param bit the position of the bit to flip (0-indexed)
+ * @return the new number after flipping the specified bit
+ */
+ public static int flipBit(final int num, final int bit) {
+ return num ^ (1 << bit);
+ }
+
+ /**
+ * Sets the bit at the specified position to 1.
+ *
+ * @param num the input number
+ * @param bit the position of the bit to set (0-indexed)
+ * @return the new number after setting the specified bit to 1
+ */
+ public static int setBit(final int num, final int bit) {
+ return num | (1 << bit);
+ }
+
+ /**
+ * Clears the bit at the specified position (sets it to 0).
+ *
+ * @param num the input number
+ * @param bit the position of the bit to clear (0-indexed)
+ * @return the new number after clearing the specified bit
+ */
+ public static int clearBit(final int num, final int bit) {
+ return num & ~(1 << bit);
+ }
+
+ /**
+ * Gets the bit value (0 or 1) at the specified position.
+ *
+ * @param num the input number
+ * @param bit the position of the bit to retrieve (0-indexed)
+ * @return 1 if the bit is set, 0 otherwise
+ */
+ public static int getBit(final int num, final int bit) {
+ return (num >> bit) & 1;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/SingleElement.java b/src/main/java/com/thealgorithms/bitmanipulation/SingleElement.java
new file mode 100644
index 000000000000..85ebdf02db25
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/SingleElement.java
@@ -0,0 +1,39 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Utility class to find the single non-duplicate element from an array
+ * where all other elements appear twice.
+ *
+ * The algorithm runs in O(n) time complexity and O(1) space complexity
+ * using bitwise XOR.
+ *
+ *
+ * @author Tuhin M
+ */
+public final class SingleElement {
+
+ /**
+ * Private constructor to prevent instantiation of this utility class.
+ * Throws an UnsupportedOperationException if attempted.
+ */
+ private SingleElement() {
+ throw new UnsupportedOperationException("Utility Class");
+ }
+
+ /**
+ * Finds the single non-duplicate element in an array where every other
+ * element appears exactly twice. Uses bitwise XOR to achieve O(n) time
+ * complexity and O(1) space complexity.
+ *
+ * @param arr the input array containing integers where every element
+ * except one appears exactly twice
+ * @return the single non-duplicate element
+ */
+ public static int findSingleElement(int[] arr) {
+ int ele = 0;
+ for (int i = 0; i < arr.length; i++) {
+ ele ^= arr[i];
+ }
+ return ele;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/SwapAdjacentBits.java b/src/main/java/com/thealgorithms/bitmanipulation/SwapAdjacentBits.java
new file mode 100644
index 000000000000..98a7de8bdf1a
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/SwapAdjacentBits.java
@@ -0,0 +1,57 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * A utility class to swap every pair of adjacent bits in a given integer.
+ * This operation shifts the even-positioned bits to odd positions and vice versa.
+ *
+ * Example:
+ * - Input: 2 (binary: `10`) → Output: 1 (binary: `01`)
+ * - Input: 43 (binary: `101011`) → Output: 23 (binary: `010111`)
+ *
+ * **Explanation of the Algorithm:**
+ * 1. Mask even-positioned bits: Using `0xAAAAAAAA` (binary: `101010...`),
+ * which selects bits in even positions.
+ * 2. Mask odd-positioned bits: Using `0x55555555` (binary: `010101...`),
+ * which selects bits in odd positions.
+ * 3. Shift bits:
+ * - Right-shift even-positioned bits by 1 to move them to odd positions.
+ * - Left-shift odd-positioned bits by 1 to move them to even positions.
+ * 4. Combine both shifted results using bitwise OR (`|`) to produce the final result.
+ *
+ * Use Case: This algorithm can be useful in applications involving low-level bit manipulation,
+ * such as encoding, data compression, or cryptographic transformations.
+ *
+ * Time Complexity: O(1) (constant time, since operations are bitwise).
+ *
+ * Author: Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ */
+public final class SwapAdjacentBits {
+ private SwapAdjacentBits() {
+ }
+
+ /**
+ * Swaps every pair of adjacent bits of a given integer.
+ * Steps:
+ * 1. Mask the even-positioned bits.
+ * 2. Mask the odd-positioned bits.
+ * 3. Shift the even bits to the right and the odd bits to the left.
+ * 4. Combine the shifted bits.
+ *
+ * @param num the integer whose bits are to be swapped
+ * @return the integer after swapping every pair of adjacent bits
+ */
+ public static int swapAdjacentBits(int num) {
+ // mask the even bits (0xAAAAAAAA => 10101010...)
+ int evenBits = num & 0xAAAAAAAA;
+
+ // mask the odd bits (0x55555555 => 01010101...)
+ int oddBits = num & 0x55555555;
+
+ // right shift even bits and left shift odd bits
+ evenBits >>= 1;
+ oddBits <<= 1;
+
+ // combine shifted bits
+ return evenBits | oddBits;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/TwosComplement.java b/src/main/java/com/thealgorithms/bitmanipulation/TwosComplement.java
new file mode 100644
index 000000000000..9b8cecd791a6
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/TwosComplement.java
@@ -0,0 +1,62 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to compute the Two's Complement of a given binary number.
+ *
+ *
In two's complement representation, a binary number's negative value is obtained
+ * by taking the one's complement (inverting all bits) and then adding 1 to the result.
+ * This method handles both small and large binary strings and ensures the output is
+ * correct for all binary inputs, including edge cases like all zeroes and all ones.
+ *
+ *
Algorithm originally suggested by Jon von Neumann.
+ *
+ * @author Abhinay Verma (https://github.com/Monk-AbhinayVerma)
+ */
+public final class TwosComplement {
+ private TwosComplement() {
+ }
+
+ /**
+ * Computes the Two's Complement of the given binary string.
+ * Steps:
+ * 1. Compute the One's Complement (invert all bits).
+ * 2. Add 1 to the One's Complement to get the Two's Complement.
+ * 3. Iterate from the rightmost bit to the left, adding 1 and carrying over as needed.
+ * 4. If a carry is still present after the leftmost bit, prepend '1' to handle overflow.
+ *
+ * @param binary The binary number as a string (only '0' and '1' characters allowed).
+ * @return The two's complement of the input binary string as a new binary string.
+ * @throws IllegalArgumentException If the input contains non-binary characters.
+ */
+ public static String twosComplement(String binary) {
+ if (!binary.matches("[01]+")) {
+ throw new IllegalArgumentException("Input must contain only '0' and '1'.");
+ }
+
+ StringBuilder onesComplement = new StringBuilder();
+ for (char bit : binary.toCharArray()) {
+ onesComplement.append(bit == '0' ? '1' : '0');
+ }
+
+ StringBuilder twosComplement = new StringBuilder(onesComplement);
+ boolean carry = true;
+
+ for (int i = onesComplement.length() - 1; i >= 0 && carry; i--) {
+ if (onesComplement.charAt(i) == '1') {
+ twosComplement.setCharAt(i, '0');
+ } else {
+ twosComplement.setCharAt(i, '1');
+ carry = false;
+ }
+ }
+
+ if (carry) {
+ twosComplement.insert(0, '1');
+ }
+
+ return twosComplement.toString();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/bitmanipulation/Xs3Conversion.java b/src/main/java/com/thealgorithms/bitmanipulation/Xs3Conversion.java
new file mode 100644
index 000000000000..b22abc0c04ff
--- /dev/null
+++ b/src/main/java/com/thealgorithms/bitmanipulation/Xs3Conversion.java
@@ -0,0 +1,58 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides methods to convert between XS-3 (Excess-3) and binary.
+ *
+ * Excess-3, also called XS-3, is a binary-coded decimal (BCD) code in which each decimal digit is represented by its corresponding 4-bit binary value plus 3.
+ *
+ * For more information, refer to the
+ * Excess-3 Wikipedia page.
+ *
+ * Example usage:
+ *
+ * int binary = Xs3Conversion.xs3ToBinary(0x4567);
+ * System.out.println("XS-3 0x4567 to binary: " + binary); // Output: 1234
+ *
+ * int xs3 = Xs3Conversion.binaryToXs3(1234);
+ * System.out.println("Binary 1234 to XS-3: " + Integer.toHexString(xs3)); // Output: 0x4567
+ *
+ */
+public final class Xs3Conversion {
+ private Xs3Conversion() {
+ }
+ /**
+ * Converts an XS-3 (Excess-3) number to binary.
+ *
+ * @param xs3 The XS-3 number.
+ * @return The corresponding binary number.
+ */
+ public static int xs3ToBinary(int xs3) {
+ int binary = 0;
+ int multiplier = 1;
+ while (xs3 > 0) {
+ int digit = (xs3 & 0xF) - 3; // Extract the last 4 bits (one XS-3 digit) and subtract 3
+ binary += digit * multiplier;
+ multiplier *= 10;
+ xs3 >>= 4; // Shift right by 4 bits to process the next XS-3 digit
+ }
+ return binary;
+ }
+
+ /**
+ * Converts a binary number to XS-3 (Excess-3).
+ *
+ * @param binary The binary number.
+ * @return The corresponding XS-3 number.
+ */
+ public static int binaryToXs3(int binary) {
+ int xs3 = 0;
+ int shift = 0;
+ while (binary > 0) {
+ int digit = (binary % 10) + 3; // Extract the last decimal digit and add 3
+ xs3 |= (digit << (shift * 4)); // Shift the digit to the correct XS-3 position
+ binary /= 10; // Remove the last decimal digit
+ shift++;
+ }
+ return xs3;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/ciphers/ADFGVXCipher.java b/src/main/java/com/thealgorithms/ciphers/ADFGVXCipher.java
new file mode 100644
index 000000000000..d915858f9e6f
--- /dev/null
+++ b/src/main/java/com/thealgorithms/ciphers/ADFGVXCipher.java
@@ -0,0 +1,167 @@
+package com.thealgorithms.ciphers;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * The ADFGVX cipher is a fractionating transposition cipher that was used by
+ * the German Army during World War I. It combines a **Polybius square substitution**
+ * with a **columnar transposition** to enhance encryption strength.
+ *
+ * The name "ADFGVX" refers to the six letters (A, D, F, G, V, X) used as row and
+ * column labels in the Polybius square. This cipher was designed to secure
+ * communication and create complex, hard-to-break ciphertexts.
+ *
+ *
+ * @author bennybebo
+ */
+public class ADFGVXCipher {
+
+ // Constants used in the Polybius square
+ private static final char[] POLYBIUS_LETTERS = {'A', 'D', 'F', 'G', 'V', 'X'};
+ private static final char[][] POLYBIUS_SQUARE = {{'N', 'A', '1', 'C', '3', 'H'}, {'8', 'T', 'B', '2', 'O', 'M'}, {'E', '5', 'W', 'R', 'P', 'D'}, {'4', 'F', '6', 'G', '7', 'I'}, {'9', 'J', '0', 'K', 'L', 'Q'}, {'S', 'U', 'V', 'X', 'Y', 'Z'}};
+
+ // Maps for fast substitution lookups
+ private static final Map POLYBIUS_MAP = new HashMap<>();
+ private static final Map REVERSE_POLYBIUS_MAP = new HashMap<>();
+
+ // Static block to initialize the lookup tables from the Polybius square
+ static {
+ for (int i = 0; i < POLYBIUS_SQUARE.length; i++) {
+ for (int j = 0; j < POLYBIUS_SQUARE[i].length; j++) {
+ String key = "" + POLYBIUS_LETTERS[i] + POLYBIUS_LETTERS[j];
+ POLYBIUS_MAP.put(key, POLYBIUS_SQUARE[i][j]);
+ REVERSE_POLYBIUS_MAP.put(POLYBIUS_SQUARE[i][j], key);
+ }
+ }
+ }
+
+ /**
+ * Encrypts a given plaintext using the ADFGVX cipher with the provided keyword.
+ * Steps:
+ * 1. Substitute each letter in the plaintext with a pair of ADFGVX letters.
+ * 2. Perform a columnar transposition on the fractionated text using the keyword.
+ *
+ * @param plaintext The message to be encrypted (can contain letters and digits).
+ * @param key The keyword for columnar transposition.
+ * @return The encrypted message as ciphertext.
+ */
+ public String encrypt(String plaintext, String key) {
+ plaintext = plaintext.toUpperCase().replaceAll("[^A-Z0-9]", ""); // Sanitize input
+ StringBuilder fractionatedText = new StringBuilder();
+
+ for (char c : plaintext.toCharArray()) {
+ fractionatedText.append(REVERSE_POLYBIUS_MAP.get(c));
+ }
+
+ return columnarTransposition(fractionatedText.toString(), key);
+ }
+
+ /**
+ * Decrypts a given ciphertext using the ADFGVX cipher with the provided keyword.
+ * Steps:
+ * 1. Reverse the columnar transposition performed during encryption.
+ * 2. Substitute each pair of ADFGVX letters with the corresponding plaintext letter.
+ * The resulting text is the decrypted message.
+ *
+ * @param ciphertext The encrypted message.
+ * @param key The keyword used during encryption.
+ * @return The decrypted plaintext message.
+ */
+ public String decrypt(String ciphertext, String key) {
+ String fractionatedText = reverseColumnarTransposition(ciphertext, key);
+
+ StringBuilder plaintext = new StringBuilder();
+ for (int i = 0; i < fractionatedText.length(); i += 2) {
+ String pair = fractionatedText.substring(i, i + 2);
+ plaintext.append(POLYBIUS_MAP.get(pair));
+ }
+
+ return plaintext.toString();
+ }
+
+ /**
+ * Helper method: Performs columnar transposition during encryption
+ *
+ * @param text The fractionated text to be transposed
+ * @param key The keyword for columnar transposition
+ * @return The transposed text
+ */
+ private String columnarTransposition(String text, String key) {
+ int numRows = (int) Math.ceil((double) text.length() / key.length());
+ char[][] table = new char[numRows][key.length()];
+ for (char[] row : table) { // Fill empty cells with underscores
+ Arrays.fill(row, '_');
+ }
+
+ // Populate the table row by row
+ for (int i = 0; i < text.length(); i++) {
+ table[i / key.length()][i % key.length()] = text.charAt(i);
+ }
+
+ // Read columns based on the alphabetical order of the key
+ StringBuilder ciphertext = new StringBuilder();
+ char[] sortedKey = key.toCharArray();
+ Arrays.sort(sortedKey);
+
+ for (char keyChar : sortedKey) {
+ int column = key.indexOf(keyChar);
+ for (char[] row : table) {
+ if (row[column] != '_') {
+ ciphertext.append(row[column]);
+ }
+ }
+ }
+
+ return ciphertext.toString();
+ }
+
+ /**
+ * Helper method: Reverses the columnar transposition during decryption
+ *
+ * @param ciphertext The transposed text to be reversed
+ * @param key The keyword used during encryption
+ * @return The reversed text
+ */
+ private String reverseColumnarTransposition(String ciphertext, String key) {
+ int numRows = (int) Math.ceil((double) ciphertext.length() / key.length());
+ char[][] table = new char[numRows][key.length()];
+
+ char[] sortedKey = key.toCharArray();
+ Arrays.sort(sortedKey);
+
+ int index = 0;
+ // Populate the table column by column according to the sorted key
+ for (char keyChar : sortedKey) {
+ int column = key.indexOf(keyChar);
+ for (int row = 0; row < numRows; row++) {
+ if (index < ciphertext.length()) {
+ table[row][column] = ciphertext.charAt(index++);
+ } else {
+ table[row][column] = '_';
+ }
+ }
+ }
+
+ // Read the table row by row to reconstruct the fractionated text
+ StringBuilder fractionatedText = new StringBuilder();
+ for (char[] row : table) {
+ for (char cell : row) {
+ if (cell != '_') {
+ fractionatedText.append(cell);
+ }
+ }
+ }
+
+ return fractionatedText.toString();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/ciphers/AES.java b/src/main/java/com/thealgorithms/ciphers/AES.java
index e310d7189b2a..1c283f6b7655 100644
--- a/src/main/java/com/thealgorithms/ciphers/AES.java
+++ b/src/main/java/com/thealgorithms/ciphers/AES.java
@@ -7,7 +7,9 @@
* This class is build to demonstrate the application of the AES-algorithm on a
* single 128-Bit block of data.
*/
-public class AES {
+public final class AES {
+ private AES() {
+ }
/**
* Precalculated values for x to the power of 2 in Rijndaels galois field.
@@ -2416,8 +2418,6 @@ public static BigInteger scheduleCore(BigInteger t, int rconCounter) {
rBytes = new StringBuilder(rBytes.substring(0, i * 2) + currentByteBits + rBytes.substring((i + 1) * 2));
}
- // t = new BigInteger(rBytes, 16);
- // return t;
return new BigInteger(rBytes.toString(), 16);
}
@@ -2754,8 +2754,8 @@ public static void main(String[] args) {
in = input.nextLine();
BigInteger encryptionKey = new BigInteger(in, 16);
System.out.println(
- "The encrypted message is: \n" +
- encrypt(plaintext, encryptionKey).toString(16)
+ "The encrypted message is: \n"
+ + encrypt(plaintext, encryptionKey).toString(16)
);
}
case 'D', 'd' -> {
@@ -2770,8 +2770,8 @@ public static void main(String[] args) {
in = input.nextLine();
BigInteger decryptionKey = new BigInteger(in, 16);
System.out.println(
- "The deciphered message is:\n" +
- decrypt(ciphertext, decryptionKey).toString(16)
+ "The deciphered message is:\n"
+ + decrypt(ciphertext, decryptionKey).toString(16)
);
}
default -> System.out.println("** End **");
diff --git a/src/main/java/com/thealgorithms/ciphers/AESEncryption.java b/src/main/java/com/thealgorithms/ciphers/AESEncryption.java
index 2b12aeaa0466..14582205442f 100644
--- a/src/main/java/com/thealgorithms/ciphers/AESEncryption.java
+++ b/src/main/java/com/thealgorithms/ciphers/AESEncryption.java
@@ -3,7 +3,12 @@
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
-import javax.crypto.*;
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.KeyGenerator;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.SecretKey;
import javax.crypto.spec.GCMParameterSpec;
/**
@@ -12,14 +17,16 @@
* hence in the following program we display it in hexadecimal format of the
* underlying bytes.
*/
-public class AESEncryption {
+public final class AESEncryption {
+ private AESEncryption() {
+ }
private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
private static Cipher aesCipher;
/**
* 1. Generate a plain text for encryption 2. Get a secret key (printed in
- * hexadecimal form). In actual use this must by encrypted and kept safe.
+ * hexadecimal form). In actual use this must be encrypted and kept safe.
* The same key is required for decryption.
*/
public static void main(String[] args) throws Exception {
diff --git a/src/main/java/com/thealgorithms/ciphers/AffineCipher.java b/src/main/java/com/thealgorithms/ciphers/AffineCipher.java
index 9ff63ddfe7c5..b82681372f2b 100644
--- a/src/main/java/com/thealgorithms/ciphers/AffineCipher.java
+++ b/src/main/java/com/thealgorithms/ciphers/AffineCipher.java
@@ -1,56 +1,87 @@
package com.thealgorithms.ciphers;
-class AffineCipher {
+/**
+ * The AffineCipher class implements the Affine cipher, a type of monoalphabetic substitution cipher.
+ * It encrypts and decrypts messages using a linear transformation defined by the formula:
+ *
+ * E(x) = (a * x + b) mod m
+ * D(y) = a^-1 * (y - b) mod m
+ *
+ * where:
+ * - E(x) is the encrypted character,
+ * - D(y) is the decrypted character,
+ * - a is the multiplicative key (must be coprime to m),
+ * - b is the additive key,
+ * - x is the index of the plaintext character,
+ * - y is the index of the ciphertext character,
+ * - m is the size of the alphabet (26 for the English alphabet).
+ *
+ * The class provides methods for encrypting and decrypting messages, as well as a main method to demonstrate its usage.
+ */
+final class AffineCipher {
+ private AffineCipher() {
+ }
// Key values of a and b
static int a = 17;
static int b = 20;
+ /**
+ * Encrypts a message using the Affine cipher.
+ *
+ * @param msg the plaintext message as a character array
+ * @return the encrypted ciphertext
+ */
static String encryptMessage(char[] msg) {
- /// Cipher Text initially empty
- String cipher = "";
+ // Cipher Text initially empty
+ StringBuilder cipher = new StringBuilder();
for (int i = 0; i < msg.length; i++) {
// Avoid space to be encrypted
- /* applying encryption formula ( a x + b ) mod m
+ /* applying encryption formula ( a * x + b ) mod m
{here x is msg[i] and m is 26} and added 'A' to
- bring it in range of ascii alphabet[ 65-90 | A-Z ] */
+ bring it in the range of ASCII alphabet [65-90 | A-Z] */
if (msg[i] != ' ') {
- cipher = cipher + (char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A');
+ cipher.append((char) ((((a * (msg[i] - 'A')) + b) % 26) + 'A'));
} else { // else simply append space character
- cipher += msg[i];
+ cipher.append(msg[i]);
}
}
- return cipher;
+ return cipher.toString();
}
+ /**
+ * Decrypts a ciphertext using the Affine cipher.
+ *
+ * @param cipher the ciphertext to decrypt
+ * @return the decrypted plaintext message
+ */
static String decryptCipher(String cipher) {
- String msg = "";
- int a_inv = 0;
- int flag = 0;
+ StringBuilder msg = new StringBuilder();
+ int aInv = 0;
+ int flag;
- // Find a^-1 (the multiplicative inverse of a
- // in the group of integers modulo m.)
+ // Find a^-1 (the multiplicative inverse of a in the group of integers modulo m.)
for (int i = 0; i < 26; i++) {
flag = (a * i) % 26;
- // Check if (a*i)%26 == 1,
+ // Check if (a * i) % 26 == 1,
// then i will be the multiplicative inverse of a
if (flag == 1) {
- a_inv = i;
+ aInv = i;
}
}
for (int i = 0; i < cipher.length(); i++) {
- /*Applying decryption formula a^-1 ( x - b ) mod m
+ /* Applying decryption formula a^-1 * (x - b) mod m
{here x is cipher[i] and m is 26} and added 'A'
- to bring it in range of ASCII alphabet[ 65-90 | A-Z ] */
+ to bring it in the range of ASCII alphabet [65-90 | A-Z] */
if (cipher.charAt(i) != ' ') {
- msg = msg + (char) (((a_inv * ((cipher.charAt(i) + 'A' - b)) % 26)) + 'A');
+ msg.append((char) (((aInv * ((cipher.charAt(i) - 'A') - b + 26)) % 26) + 'A'));
} else { // else simply append space character
- msg += cipher.charAt(i);
+ msg.append(cipher.charAt(i));
}
}
- return msg;
+ return msg.toString();
}
// Driver code
diff --git a/src/main/java/com/thealgorithms/ciphers/AtbashCipher.java b/src/main/java/com/thealgorithms/ciphers/AtbashCipher.java
new file mode 100644
index 000000000000..9169aa82bd75
--- /dev/null
+++ b/src/main/java/com/thealgorithms/ciphers/AtbashCipher.java
@@ -0,0 +1,101 @@
+package com.thealgorithms.ciphers;
+
+/**
+ * The Atbash cipher is a classic substitution cipher that substitutes each letter
+ * with its opposite letter in the alphabet.
+ *
+ * For example:
+ * - 'A' becomes 'Z', 'B' becomes 'Y', 'C' becomes 'X', and so on.
+ * - Similarly, 'a' becomes 'z', 'b' becomes 'y', and so on.
+ *
+ * The cipher works identically for both uppercase and lowercase letters.
+ * Non-alphabetical characters remain unchanged in the output.
+ *
+ * This cipher is symmetric, meaning that applying the cipher twice will return
+ * the original text. Therefore, the same function is used for both encryption and decryption.
+ *
+ *
+ *
+ * Note: The key size directly affects the security and performance of the RSA algorithm.
+ * Larger keys are more secure but slower to compute.
+ *
+ * @author Nguyen Duy Tiep
+ * @version 23-Oct-17
*/
public class RSA {
@@ -12,55 +32,88 @@ public class RSA {
private BigInteger privateKey;
private BigInteger publicKey;
+ /**
+ * Constructor that generates RSA keys with the specified number of bits.
+ *
+ * @param bits The bit length of the keys to be generated. Common sizes include 512, 1024, 2048, etc.
+ */
public RSA(int bits) {
generateKeys(bits);
}
/**
- * @return encrypted message
+ * Encrypts a text message using the RSA public key.
+ *
+ * @param message The plaintext message to be encrypted.
+ * @throws IllegalArgumentException If the message is empty.
+ * @return The encrypted message represented as a String.
*/
public synchronized String encrypt(String message) {
+ if (message.isEmpty()) {
+ throw new IllegalArgumentException("Message is empty");
+ }
return (new BigInteger(message.getBytes())).modPow(publicKey, modulus).toString();
}
/**
- * @return encrypted message as big integer
+ * Encrypts a BigInteger message using the RSA public key.
+ *
+ * @param message The plaintext message as a BigInteger.
+ * @return The encrypted message as a BigInteger.
*/
public synchronized BigInteger encrypt(BigInteger message) {
return message.modPow(publicKey, modulus);
}
/**
- * @return plain message
+ * Decrypts an encrypted message (as String) using the RSA private key.
+ *
+ * @param encryptedMessage The encrypted message to be decrypted, represented as a String.
+ * @throws IllegalArgumentException If the message is empty.
+ * @return The decrypted plaintext message as a String.
*/
public synchronized String decrypt(String encryptedMessage) {
+ if (encryptedMessage.isEmpty()) {
+ throw new IllegalArgumentException("Message is empty");
+ }
return new String((new BigInteger(encryptedMessage)).modPow(privateKey, modulus).toByteArray());
}
/**
- * @return plain message as big integer
+ * Decrypts an encrypted BigInteger message using the RSA private key.
+ *
+ * @param encryptedMessage The encrypted message as a BigInteger.
+ * @return The decrypted plaintext message as a BigInteger.
*/
public synchronized BigInteger decrypt(BigInteger encryptedMessage) {
return encryptedMessage.modPow(privateKey, modulus);
}
/**
- * Generate a new public and private key set.
+ * Generates a new RSA key pair (public and private keys) with the specified bit length.
+ * Steps:
+ * 1. Generate two large prime numbers p and q.
+ * 2. Compute the modulus n = p * q.
+ * 3. Compute Euler's totient function: φ(n) = (p-1) * (q-1).
+ * 4. Choose a public key e (starting from 3) that is coprime with φ(n).
+ * 5. Compute the private key d as the modular inverse of e mod φ(n).
+ * The public key is (e, n) and the private key is (d, n).
+ *
+ * @param bits The bit length of the keys to be generated.
*/
- public synchronized void generateKeys(int bits) {
- SecureRandom r = new SecureRandom();
- BigInteger p = new BigInteger(bits / 2, 100, r);
- BigInteger q = new BigInteger(bits / 2, 100, r);
+ public final synchronized void generateKeys(int bits) {
+ SecureRandom random = new SecureRandom();
+ BigInteger p = new BigInteger(bits / 2, 100, random);
+ BigInteger q = new BigInteger(bits / 2, 100, random);
modulus = p.multiply(q);
- BigInteger m = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
+ BigInteger phi = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
publicKey = BigInteger.valueOf(3L);
-
- while (m.gcd(publicKey).intValue() > 1) {
+ while (phi.gcd(publicKey).intValue() > 1) {
publicKey = publicKey.add(BigInteger.TWO);
}
- privateKey = publicKey.modInverse(m);
+ privateKey = publicKey.modInverse(phi);
}
}
diff --git a/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java b/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java
new file mode 100644
index 000000000000..f81252980468
--- /dev/null
+++ b/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java
@@ -0,0 +1,147 @@
+package com.thealgorithms.ciphers;
+
+import java.util.Arrays;
+
+/**
+ * The rail fence cipher (also called a zigzag cipher) is a classical type of transposition cipher.
+ * It derives its name from the manner in which encryption is performed, in analogy to a fence built with horizontal rails.
+ * https://en.wikipedia.org/wiki/Rail_fence_cipher
+ * @author https://github.com/Krounosity
+ */
+
+public class RailFenceCipher {
+
+ // Encrypts the input string using the rail fence cipher method with the given number of rails.
+ public String encrypt(String str, int rails) {
+
+ // Base case of single rail or rails are more than the number of characters in the string
+ if (rails == 1 || rails >= str.length()) {
+ return str;
+ }
+
+ // Boolean flag to determine if the movement is downward or upward in the rail matrix.
+ boolean down = true;
+ // Create a 2D array to represent the rails (rows) and the length of the string (columns).
+ char[][] strRail = new char[rails][str.length()];
+
+ // Initialize all positions in the rail matrix with a placeholder character ('\n').
+ for (int i = 0; i < rails; i++) {
+ Arrays.fill(strRail[i], '\n');
+ }
+
+ int row = 0; // Start at the first row
+ int col = 0; // Start at the first column
+
+ int i = 0;
+
+ // Fill the rail matrix with characters from the string based on the rail pattern.
+ while (col < str.length()) {
+ // Change direction to down when at the first row.
+ if (row == 0) {
+ down = true;
+ }
+ // Change direction to up when at the last row.
+ else if (row == rails - 1) {
+ down = false;
+ }
+
+ // Place the character in the current position of the rail matrix.
+ strRail[row][col] = str.charAt(i);
+ col++; // Move to the next column.
+ // Move to the next row based on the direction.
+ if (down) {
+ row++;
+ } else {
+ row--;
+ }
+
+ i++;
+ }
+
+ // Construct the encrypted string by reading characters row by row.
+ StringBuilder encryptedString = new StringBuilder();
+ for (char[] chRow : strRail) {
+ for (char ch : chRow) {
+ if (ch != '\n') {
+ encryptedString.append(ch);
+ }
+ }
+ }
+ return encryptedString.toString();
+ }
+ // Decrypts the input string using the rail fence cipher method with the given number of rails.
+ public String decrypt(String str, int rails) {
+
+ // Base case of single rail or rails are more than the number of characters in the string
+ if (rails == 1 || rails >= str.length()) {
+ return str;
+ }
+ // Boolean flag to determine if the movement is downward or upward in the rail matrix.
+ boolean down = true;
+
+ // Create a 2D array to represent the rails (rows) and the length of the string (columns).
+ char[][] strRail = new char[rails][str.length()];
+
+ int row = 0; // Start at the first row
+ int col = 0; // Start at the first column
+
+ // Mark the pattern on the rail matrix using '*'.
+ while (col < str.length()) {
+ // Change direction to down when at the first row.
+ if (row == 0) {
+ down = true;
+ }
+ // Change direction to up when at the last row.
+ else if (row == rails - 1) {
+ down = false;
+ }
+
+ // Mark the current position in the rail matrix.
+ strRail[row][col] = '*';
+ col++; // Move to the next column.
+ // Move to the next row based on the direction.
+ if (down) {
+ row++;
+ } else {
+ row--;
+ }
+ }
+
+ int index = 0; // Index to track characters from the input string.
+ // Fill the rail matrix with characters from the input string based on the marked pattern.
+ for (int i = 0; i < rails; i++) {
+ for (int j = 0; j < str.length(); j++) {
+ if (strRail[i][j] == '*') {
+ strRail[i][j] = str.charAt(index++);
+ }
+ }
+ }
+
+ // Construct the decrypted string by following the zigzag pattern.
+ StringBuilder decryptedString = new StringBuilder();
+ row = 0; // Reset to the first row
+ col = 0; // Reset to the first column
+
+ while (col < str.length()) {
+ // Change direction to down when at the first row.
+ if (row == 0) {
+ down = true;
+ }
+ // Change direction to up when at the last row.
+ else if (row == rails - 1) {
+ down = false;
+ }
+ // Append the character from the rail matrix to the decrypted string.
+ decryptedString.append(strRail[row][col]);
+ col++; // Move to the next column.
+ // Move to the next row based on the direction.
+ if (down) {
+ row++;
+ } else {
+ row--;
+ }
+ }
+
+ return decryptedString.toString();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/ciphers/SimpleSubstitutionCipher.java b/src/main/java/com/thealgorithms/ciphers/SimpleSubstitutionCipher.java
deleted file mode 100644
index 6ce3c564abc7..000000000000
--- a/src/main/java/com/thealgorithms/ciphers/SimpleSubstitutionCipher.java
+++ /dev/null
@@ -1,83 +0,0 @@
-package com.thealgorithms.ciphers;
-
-import java.util.HashMap;
-import java.util.Map;
-
-/**
- * The simple substitution cipher is a cipher that has been in use for many
- * hundreds of years (an excellent history is given in Simon Singhs 'the Code
- * Book'). It basically consists of substituting every plaintext character for a
- * different ciphertext character. It differs from the Caesar cipher in that the
- * cipher alphabet is not simply the alphabet shifted, it is completely jumbled.
- *
- * @author Hassan Elseoudy
- */
-public class SimpleSubstitutionCipher {
-
- /**
- * Encrypt text by replacing each element with its opposite character.
- *
- * @return Encrypted message
- */
- public static String encode(String message, String cipherSmall) {
- StringBuilder encoded = new StringBuilder();
-
- // This map is used to encode
- Map cipherMap = new HashMap<>();
-
- char beginSmallLetter = 'a';
- char beginCapitalLetter = 'A';
-
- cipherSmall = cipherSmall.toLowerCase();
- String cipherCapital = cipherSmall.toUpperCase();
-
- // To handle Small and Capital letters
- for (int i = 0; i < cipherSmall.length(); i++) {
- cipherMap.put(beginSmallLetter++, cipherSmall.charAt(i));
- cipherMap.put(beginCapitalLetter++, cipherCapital.charAt(i));
- }
-
- for (int i = 0; i < message.length(); i++) {
- if (Character.isAlphabetic(message.charAt(i))) {
- encoded.append(cipherMap.get(message.charAt(i)));
- } else {
- encoded.append(message.charAt(i));
- }
- }
-
- return encoded.toString();
- }
-
- /**
- * Decrypt message by replacing each element with its opposite character in
- * cipher.
- *
- * @return message
- */
- public static String decode(String encryptedMessage, String cipherSmall) {
- StringBuilder decoded = new StringBuilder();
-
- Map cipherMap = new HashMap<>();
-
- char beginSmallLetter = 'a';
- char beginCapitalLetter = 'A';
-
- cipherSmall = cipherSmall.toLowerCase();
- String cipherCapital = cipherSmall.toUpperCase();
-
- for (int i = 0; i < cipherSmall.length(); i++) {
- cipherMap.put(cipherSmall.charAt(i), beginSmallLetter++);
- cipherMap.put(cipherCapital.charAt(i), beginCapitalLetter++);
- }
-
- for (int i = 0; i < encryptedMessage.length(); i++) {
- if (Character.isAlphabetic(encryptedMessage.charAt(i))) {
- decoded.append(cipherMap.get(encryptedMessage.charAt(i)));
- } else {
- decoded.append(encryptedMessage.charAt(i));
- }
- }
-
- return decoded.toString();
- }
-}
diff --git a/src/main/java/com/thealgorithms/ciphers/Vigenere.java b/src/main/java/com/thealgorithms/ciphers/Vigenere.java
index 1702f1abb94c..0f117853bb85 100644
--- a/src/main/java/com/thealgorithms/ciphers/Vigenere.java
+++ b/src/main/java/com/thealgorithms/ciphers/Vigenere.java
@@ -1,16 +1,54 @@
package com.thealgorithms.ciphers;
/**
- * A Java implementation of Vigenere Cipher.
+ * A Java implementation of the Vigenère Cipher.
+ *
+ * The Vigenère Cipher is a polyalphabetic substitution cipher that uses a
+ * keyword to shift letters in the plaintext by different amounts, depending
+ * on the corresponding character in the keyword. It wraps around the alphabet,
+ * ensuring the shifts are within 'A'-'Z' or 'a'-'z'.
+ *
+ * Non-alphabetic characters (like spaces, punctuation) are kept unchanged.
+ *
+ * Encryption Example:
+ * - Plaintext: "Hello World!"
+ * - Key: "suchsecret"
+ * - Encrypted Text: "Zynsg Yfvev!"
+ *
+ * Decryption Example:
+ * - Ciphertext: "Zynsg Yfvev!"
+ * - Key: "suchsecret"
+ * - Decrypted Text: "Hello World!"
+ *
+ * Wikipedia Reference:
+ * Vigenère Cipher - Wikipedia
*
* @author straiffix
* @author beingmartinbmc
*/
public class Vigenere {
+ /**
+ * Encrypts a given message using the Vigenère Cipher with the specified key.
+ * Steps:
+ * 1. Iterate over each character in the message.
+ * 2. If the character is a letter, shift it by the corresponding character in the key.
+ * 3. Preserve the case of the letter.
+ * 4. Preserve non-alphabetic characters.
+ * 5. Move to the next character in the key (cyclic).
+ * 6. Return the encrypted message.
+ *
+ * @param message The plaintext message to encrypt.
+ * @param key The keyword used for encryption.
+ * @throws IllegalArgumentException if the key is empty.
+ * @return The encrypted message.
+ */
public String encrypt(final String message, final String key) {
- StringBuilder result = new StringBuilder();
+ if (key.isEmpty()) {
+ throw new IllegalArgumentException("Key cannot be empty.");
+ }
+ StringBuilder result = new StringBuilder();
int j = 0;
for (int i = 0; i < message.length(); i++) {
char c = message.charAt(i);
@@ -20,17 +58,35 @@ public String encrypt(final String message, final String key) {
} else {
result.append((char) ((c + key.toLowerCase().charAt(j) - 2 * 'a') % 26 + 'a'));
}
+ j = ++j % key.length();
} else {
result.append(c);
}
- j = ++j % key.length();
}
return result.toString();
}
+ /**
+ * Decrypts a given message encrypted with the Vigenère Cipher using the specified key.
+ * Steps:
+ * 1. Iterate over each character in the message.
+ * 2. If the character is a letter, shift it back by the corresponding character in the key.
+ * 3. Preserve the case of the letter.
+ * 4. Preserve non-alphabetic characters.
+ * 5. Move to the next character in the key (cyclic).
+ * 6. Return the decrypted message.
+ *
+ * @param message The encrypted message to decrypt.
+ * @param key The keyword used for decryption.
+ * @throws IllegalArgumentException if the key is empty.
+ * @return The decrypted plaintext message.
+ */
public String decrypt(final String message, final String key) {
- StringBuilder result = new StringBuilder();
+ if (key.isEmpty()) {
+ throw new IllegalArgumentException("Key cannot be empty.");
+ }
+ StringBuilder result = new StringBuilder();
int j = 0;
for (int i = 0; i < message.length(); i++) {
char c = message.charAt(i);
@@ -40,11 +96,10 @@ public String decrypt(final String message, final String key) {
} else {
result.append((char) ('z' - (25 - (c - key.toLowerCase().charAt(j))) % 26));
}
+ j = ++j % key.length();
} else {
result.append(c);
}
-
- j = ++j % key.length();
}
return result.toString();
}
diff --git a/src/main/java/com/thealgorithms/ciphers/XORCipher.java b/src/main/java/com/thealgorithms/ciphers/XORCipher.java
new file mode 100644
index 000000000000..a612ccfbcdef
--- /dev/null
+++ b/src/main/java/com/thealgorithms/ciphers/XORCipher.java
@@ -0,0 +1,95 @@
+package com.thealgorithms.ciphers;
+
+import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
+import java.util.HexFormat;
+
+/**
+ * A simple implementation of the XOR cipher that allows both encryption and decryption
+ * using a given key. This cipher works by applying the XOR bitwise operation between
+ * the bytes of the input text and the corresponding bytes of the key (repeating the key
+ * if necessary).
+ *
+ * Usage:
+ * - Encryption: Converts plaintext into a hexadecimal-encoded ciphertext.
+ * - Decryption: Converts the hexadecimal ciphertext back into plaintext.
+ *
+ * Characteristics:
+ * - Symmetric: The same key is used for both encryption and decryption.
+ * - Simple but vulnerable: XOR encryption is insecure for real-world cryptography,
+ * especially when the same key is reused.
+ *
+ * Example:
+ * Plaintext: "Hello!"
+ * Key: "key"
+ * Encrypted: "27090c03120b"
+ * Decrypted: "Hello!"
+ *
+ * Reference: XOR Cipher - Wikipedia
+ *
+ * @author lcsjunior
+ */
+public final class XORCipher {
+
+ // Default character encoding for string conversion
+ private static final Charset CS_DEFAULT = StandardCharsets.UTF_8;
+
+ private XORCipher() {
+ }
+
+ /**
+ * Applies the XOR operation between the input bytes and the key bytes.
+ * If the key is shorter than the input, it wraps around (cyclically).
+ *
+ * @param inputBytes The input byte array (plaintext or ciphertext).
+ * @param keyBytes The key byte array used for XOR operation.
+ * @return A new byte array containing the XOR result.
+ */
+ public static byte[] xor(final byte[] inputBytes, final byte[] keyBytes) {
+ byte[] outputBytes = new byte[inputBytes.length];
+ for (int i = 0; i < inputBytes.length; ++i) {
+ outputBytes[i] = (byte) (inputBytes[i] ^ keyBytes[i % keyBytes.length]);
+ }
+ return outputBytes;
+ }
+
+ /**
+ * Encrypts the given plaintext using the XOR cipher with the specified key.
+ * The result is a hexadecimal-encoded string representing the ciphertext.
+ *
+ * @param plainText The input plaintext to encrypt.
+ * @param key The encryption key.
+ * @throws IllegalArgumentException if the key is empty.
+ * @return A hexadecimal string representing the encrypted text.
+ */
+ public static String encrypt(final String plainText, final String key) {
+ if (key.isEmpty()) {
+ throw new IllegalArgumentException("Key must not be empty");
+ }
+
+ byte[] plainTextBytes = plainText.getBytes(CS_DEFAULT);
+ byte[] keyBytes = key.getBytes(CS_DEFAULT);
+ byte[] xorResult = xor(plainTextBytes, keyBytes);
+ return HexFormat.of().formatHex(xorResult);
+ }
+
+ /**
+ * Decrypts the given ciphertext (in hexadecimal format) using the XOR cipher
+ * with the specified key. The result is the original plaintext.
+ *
+ * @param cipherText The hexadecimal string representing the encrypted text.
+ * @param key The decryption key (must be the same as the encryption key).
+ * @throws IllegalArgumentException if the key is empty.
+ * @return The decrypted plaintext.
+ */
+ public static String decrypt(final String cipherText, final String key) {
+ if (key.isEmpty()) {
+ throw new IllegalArgumentException("Key must not be empty");
+ }
+
+ byte[] cipherBytes = HexFormat.of().parseHex(cipherText);
+ byte[] keyBytes = key.getBytes(CS_DEFAULT);
+ byte[] xorResult = xor(cipherBytes, keyBytes);
+ return new String(xorResult, CS_DEFAULT);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/ciphers/a5/A5Cipher.java b/src/main/java/com/thealgorithms/ciphers/a5/A5Cipher.java
index b7d36db5c809..cc2e9105229a 100644
--- a/src/main/java/com/thealgorithms/ciphers/a5/A5Cipher.java
+++ b/src/main/java/com/thealgorithms/ciphers/a5/A5Cipher.java
@@ -2,17 +2,43 @@
import java.util.BitSet;
-// https://en.wikipedia.org/wiki/A5/1
+/**
+ * The A5Cipher class implements the A5/1 stream cipher, which is a widely used
+ * encryption algorithm, particularly in mobile communications.
+ *
+ * This implementation uses a key stream generator to produce a stream of bits
+ * that are XORed with the plaintext bits to produce the ciphertext.
+ *
+ *
+ * For more details about the A5/1 algorithm, refer to
+ * Wikipedia.
+ *
+ */
public class A5Cipher {
private final A5KeyStreamGenerator keyStreamGenerator;
- private static final int KEY_STREAM_LENGTH = 228; // 28.5 bytes so we need to pad bytes or something
-
+ private static final int KEY_STREAM_LENGTH = 228; // Length of the key stream in bits (28.5 bytes)
+
+ /**
+ * Constructs an A5Cipher instance with the specified session key and frame counter.
+ *
+ * @param sessionKey a BitSet representing the session key used for encryption.
+ * @param frameCounter a BitSet representing the frame counter that helps in key stream generation.
+ */
public A5Cipher(BitSet sessionKey, BitSet frameCounter) {
keyStreamGenerator = new A5KeyStreamGenerator();
keyStreamGenerator.initialize(sessionKey, frameCounter);
}
+ /**
+ * Encrypts the given plaintext bits using the A5/1 cipher algorithm.
+ *
+ * This method generates a key stream and XORs it with the provided plaintext
+ * bits to produce the ciphertext.
+ *
+ * @param plainTextBits a BitSet representing the plaintext bits to be encrypted.
+ * @return a BitSet containing the encrypted ciphertext bits.
+ */
public BitSet encrypt(BitSet plainTextBits) {
// create a copy
var result = new BitSet(KEY_STREAM_LENGTH);
@@ -24,6 +50,13 @@ public BitSet encrypt(BitSet plainTextBits) {
return result;
}
+ /**
+ * Resets the internal counter of the key stream generator.
+ *
+ * This method can be called to re-initialize the state of the key stream
+ * generator, allowing for new key streams to be generated for subsequent
+ * encryptions.
+ */
public void resetCounter() {
keyStreamGenerator.reInitialize();
}
diff --git a/src/main/java/com/thealgorithms/ciphers/a5/A5KeyStreamGenerator.java b/src/main/java/com/thealgorithms/ciphers/a5/A5KeyStreamGenerator.java
index 2e92498056ae..ee837ef4241a 100644
--- a/src/main/java/com/thealgorithms/ciphers/a5/A5KeyStreamGenerator.java
+++ b/src/main/java/com/thealgorithms/ciphers/a5/A5KeyStreamGenerator.java
@@ -2,15 +2,39 @@
import java.util.BitSet;
-// TODO: raise exceptions for improper use
+/**
+ * The A5KeyStreamGenerator class is responsible for generating key streams
+ * for the A5/1 encryption algorithm using a combination of Linear Feedback Shift Registers (LFSRs).
+ *
+ *
+ * This class extends the CompositeLFSR and initializes a set of LFSRs with
+ * a session key and a frame counter to produce a pseudo-random key stream.
+ *
+ *
+ *
+ * Note: Proper exception handling for invalid usage is to be implemented.
+ *
+ */
public class A5KeyStreamGenerator extends CompositeLFSR {
private BitSet initialFrameCounter;
private BitSet frameCounter;
private BitSet sessionKey;
private static final int INITIAL_CLOCKING_CYCLES = 100;
- private static final int KEY_STREAM_LENGTH = 228; // 28.5 bytes so we need to pad bytes or something
+ private static final int KEY_STREAM_LENGTH = 228;
+ /**
+ * Initializes the A5KeyStreamGenerator with the specified session key and frame counter.
+ *
+ *
+ * This method sets up the internal state of the LFSRs using the provided
+ * session key and frame counter. It creates three LFSRs with specific
+ * configurations and initializes them.
+ *
+ *
+ * @param sessionKey a BitSet representing the session key used for key stream generation.
+ * @param frameCounter a BitSet representing the frame counter that influences the key stream.
+ */
@Override
public void initialize(BitSet sessionKey, BitSet frameCounter) {
this.sessionKey = sessionKey;
@@ -26,12 +50,30 @@ public void initialize(BitSet sessionKey, BitSet frameCounter) {
registers.forEach(lfsr -> lfsr.initialize(sessionKey, frameCounter));
}
+ /**
+ * Re-initializes the key stream generator with the original session key
+ * and frame counter. This method restores the generator to its initial
+ * state.
+ */
public void reInitialize() {
this.initialize(sessionKey, initialFrameCounter);
}
+ /**
+ * Generates the next key stream of bits.
+ *
+ *
+ * This method performs an initial set of clocking cycles and then retrieves
+ * a key stream of the specified length. After generation, it re-initializes
+ * the internal registers.
+ *
+ *
+ * @return a BitSet containing the generated key stream bits.
+ */
public BitSet getNextKeyStream() {
- for (int cycle = 1; cycle <= INITIAL_CLOCKING_CYCLES; ++cycle) this.clock();
+ for (int cycle = 1; cycle <= INITIAL_CLOCKING_CYCLES; ++cycle) {
+ this.clock();
+ }
BitSet result = new BitSet(KEY_STREAM_LENGTH);
for (int cycle = 1; cycle <= KEY_STREAM_LENGTH; ++cycle) {
@@ -43,12 +85,37 @@ public BitSet getNextKeyStream() {
return result;
}
+ /**
+ * Re-initializes the registers for the LFSRs.
+ *
+ *
+ * This method increments the frame counter and re-initializes each LFSR
+ * with the current session key and frame counter.
+ *
+ * This method uses a utility function to increment the frame counter,
+ * which influences the key stream generation process.
+ *
+ */
private void incrementFrameCounter() {
Utils.increment(frameCounter, FRAME_COUNTER_LENGTH);
}
+
+ /**
+ * Retrieves the current frame counter.
+ *
+ * @return a BitSet representing the current state of the frame counter.
+ */
+ public BitSet getFrameCounter() {
+ return frameCounter;
+ }
}
diff --git a/src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java b/src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java
index 12e93717a3de..029a93848c28 100644
--- a/src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java
+++ b/src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java
@@ -5,13 +5,33 @@
import java.util.Map;
import java.util.TreeMap;
+/**
+ * The CompositeLFSR class represents a composite implementation of
+ * Linear Feedback Shift Registers (LFSRs) for cryptographic purposes.
+ *
+ *
+ * This abstract class manages a collection of LFSR instances and
+ * provides a mechanism for irregular clocking based on the
+ * majority bit among the registers. It implements the BaseLFSR
+ * interface, requiring subclasses to define specific LFSR behaviors.
+ *
+ */
public abstract class CompositeLFSR implements BaseLFSR {
protected final List registers = new ArrayList<>();
/**
- * Implements irregular clocking using the clock bit for each register
- * @return the registers discarded bit xored value
+ * Performs a clocking operation on the composite LFSR.
+ *
+ *
+ * This method determines the majority bit across all registers and
+ * clocks each register based on its clock bit. If a register's
+ * clock bit matches the majority bit, it is clocked (shifted).
+ * The method also computes and returns the XOR of the last bits
+ * of all registers.
+ *
+ *
+ * @return the XOR value of the last bits of all registers.
*/
@Override
public boolean clock() {
@@ -19,17 +39,31 @@ public boolean clock() {
boolean result = false;
for (var register : registers) {
result ^= register.getLastBit();
- if (register.getClockBit() == majorityBit) register.clock();
+ if (register.getClockBit() == majorityBit) {
+ register.clock();
+ }
}
return result;
}
+ /**
+ * Calculates the majority bit among all registers.
+ *
+ *
+ * This private method counts the number of true and false clock bits
+ * across all LFSR registers. It returns true if the count of true
+ * bits is greater than or equal to the count of false bits; otherwise,
+ * it returns false.
+ *
+ *
+ * @return true if the majority clock bits are true; false otherwise.
+ */
private boolean getMajorityBit() {
Map bitCount = new TreeMap<>();
- bitCount.put(false, 0);
- bitCount.put(true, 0);
+ bitCount.put(Boolean.FALSE, 0);
+ bitCount.put(Boolean.TRUE, 0);
registers.forEach(lfsr -> bitCount.put(lfsr.getClockBit(), bitCount.get(lfsr.getClockBit()) + 1));
- return bitCount.get(false) <= bitCount.get(true);
+ return bitCount.get(Boolean.FALSE) <= bitCount.get(Boolean.TRUE);
}
}
diff --git a/src/main/java/com/thealgorithms/ciphers/a5/Utils.java b/src/main/java/com/thealgorithms/ciphers/a5/Utils.java
index abdd11d6b72d..b4addf18dd9d 100644
--- a/src/main/java/com/thealgorithms/ciphers/a5/Utils.java
+++ b/src/main/java/com/thealgorithms/ciphers/a5/Utils.java
@@ -7,7 +7,9 @@
import java.util.BitSet;
-public class Utils {
+public final class Utils {
+ private Utils() {
+ }
public static boolean increment(BitSet bits, int size) {
int i = size - 1;
diff --git a/src/main/java/com/thealgorithms/conversions/AffineConverter.java b/src/main/java/com/thealgorithms/conversions/AffineConverter.java
new file mode 100644
index 000000000000..199a6dd517d5
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/AffineConverter.java
@@ -0,0 +1,64 @@
+package com.thealgorithms.conversions;
+
+/**
+ * A utility class to perform affine transformations of the form:
+ * y = slope * x + intercept.
+ *
+ * This class supports inversion and composition of affine transformations.
+ * It is immutable, meaning each instance represents a fixed transformation.
+ */
+public final class AffineConverter {
+ private final double slope;
+ private final double intercept;
+
+ /**
+ * Constructs an AffineConverter with the given slope and intercept.
+ *
+ * @param inSlope The slope of the affine transformation.
+ * @param inIntercept The intercept (constant term) of the affine transformation.
+ * @throws IllegalArgumentException if either parameter is NaN.
+ */
+ public AffineConverter(final double inSlope, final double inIntercept) {
+ if (Double.isNaN(inSlope) || Double.isNaN(inIntercept)) {
+ throw new IllegalArgumentException("Slope and intercept must be valid numbers.");
+ }
+ slope = inSlope;
+ intercept = inIntercept;
+ }
+
+ /**
+ * Converts the given input value using the affine transformation:
+ * result = slope * inValue + intercept.
+ *
+ * @param inValue The input value to convert.
+ * @return The transformed value.
+ */
+ public double convert(final double inValue) {
+ return slope * inValue + intercept;
+ }
+
+ /**
+ * Returns a new AffineConverter representing the inverse of the current transformation.
+ * The inverse of y = slope * x + intercept is x = (y - intercept) / slope.
+ *
+ * @return A new AffineConverter representing the inverse transformation.
+ * @throws AssertionError if the slope is zero, as the inverse would be undefined.
+ */
+ public AffineConverter invert() {
+ assert slope != 0.0 : "Slope cannot be zero for inversion.";
+ return new AffineConverter(1.0 / slope, -intercept / slope);
+ }
+
+ /**
+ * Composes this affine transformation with another, returning a new AffineConverter.
+ * If this transformation is f(x) and the other is g(x), the result is f(g(x)).
+ *
+ * @param other Another AffineConverter to compose with.
+ * @return A new AffineConverter representing the composition of the two transformations.
+ */
+ public AffineConverter compose(final AffineConverter other) {
+ double newSlope = slope * other.slope;
+ double newIntercept = slope * other.intercept + intercept;
+ return new AffineConverter(newSlope, newIntercept);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java b/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
index 7a87fd15be23..7a9448fd8fe7 100644
--- a/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
+++ b/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
@@ -13,7 +13,9 @@
* @author Michael Rolland
* @version 2017.10.10
*/
-public class AnyBaseToAnyBase {
+public final class AnyBaseToAnyBase {
+ private AnyBaseToAnyBase() {
+ }
/**
* Smallest and largest base you want to accept as valid input
@@ -25,7 +27,8 @@ public class AnyBaseToAnyBase {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String n;
- int b1, b2;
+ int b1;
+ int b2;
while (true) {
try {
System.out.print("Enter number: ");
@@ -130,9 +133,10 @@ public static String base2base(String n, int b1, int b2) {
// Declare variables: decimal value of n,
// character of base b1, character of base b2,
// and the string that will be returned.
- int decimalValue = 0, charB2;
+ int decimalValue = 0;
+ int charB2;
char charB1;
- String output = "";
+ StringBuilder output = new StringBuilder();
// Go through every character of n
for (int i = 0; i < n.length(); i++) {
// store the character in charB1
@@ -163,15 +167,15 @@ public static String base2base(String n, int b1, int b2) {
// If the remainder is a digit < 10, simply add it to
// the left side of the new number.
if (decimalValue % b2 < 10) {
- output = decimalValue % b2 + output;
+ output.insert(0, decimalValue % b2);
} // If the remainder is >= 10, add a character with the
// corresponding value to the new number. (A = 10, B = 11, C = 12, ...)
else {
- output = (char) ((decimalValue % b2) + 55) + output;
+ output.insert(0, (char) ((decimalValue % b2) + 55));
}
// Divide by the new base again
decimalValue /= b2;
}
- return output;
+ return output.toString();
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/AnyBaseToDecimal.java b/src/main/java/com/thealgorithms/conversions/AnyBaseToDecimal.java
index 837b35305c80..cdab98c7c28a 100644
--- a/src/main/java/com/thealgorithms/conversions/AnyBaseToDecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/AnyBaseToDecimal.java
@@ -1,54 +1,52 @@
package com.thealgorithms.conversions;
/**
- * @author Varun Upadhyay (https://github.com/varunu28)
+ * @author Varun Upadhyay (...)
*/
-// Driver program
-public class AnyBaseToDecimal {
+public final class AnyBaseToDecimal {
+ private static final int CHAR_OFFSET_FOR_DIGIT = '0';
+ private static final int CHAR_OFFSET_FOR_UPPERCASE = 'A' - 10;
- public static void main(String[] args) {
- assert convertToDecimal("1010", 2) == Integer.valueOf("1010", 2);
- assert convertToDecimal("777", 8) == Integer.valueOf("777", 8);
- assert convertToDecimal("999", 10) == Integer.valueOf("999", 10);
- assert convertToDecimal("ABCDEF", 16) == Integer.valueOf("ABCDEF", 16);
- assert convertToDecimal("XYZ", 36) == Integer.valueOf("XYZ", 36);
+ private AnyBaseToDecimal() {
}
/**
- * Convert any radix to decimal number
+ * Convert any radix to a decimal number.
*
- * @param s the string to be convert
- * @param radix the radix
- * @return decimal of bits
- * @throws NumberFormatException if {@code bits} or {@code radix} is invalid
+ * @param input the string to be converted
+ * @param radix the radix (base) of the input string
+ * @return the decimal equivalent of the input string
+ * @throws NumberFormatException if the input string or radix is invalid
*/
- public static int convertToDecimal(String s, int radix) {
- int num = 0;
- int pow = 1;
+ public static int convertToDecimal(String input, int radix) {
+ int result = 0;
+ int power = 1;
- for (int i = s.length() - 1; i >= 0; i--) {
- int digit = valOfChar(s.charAt(i));
+ for (int i = input.length() - 1; i >= 0; i--) {
+ int digit = valOfChar(input.charAt(i));
if (digit >= radix) {
- throw new NumberFormatException("For input string " + s);
+ throw new NumberFormatException("For input string: " + input);
}
- num += valOfChar(s.charAt(i)) * pow;
- pow *= radix;
+ result += digit * power;
+ power *= radix;
}
- return num;
+ return result;
}
/**
- * Convert character to integer
+ * Convert a character to its integer value.
*
- * @param c the character
- * @return represented digit of given character
- * @throws NumberFormatException if {@code ch} is not UpperCase or Digit
- * character.
+ * @param character the character to be converted
+ * @return the integer value represented by the character
+ * @throws NumberFormatException if the character is not an uppercase letter or a digit
*/
- public static int valOfChar(char c) {
- if (!(Character.isUpperCase(c) || Character.isDigit(c))) {
- throw new NumberFormatException("invalid character :" + c);
+ private static int valOfChar(char character) {
+ if (Character.isDigit(character)) {
+ return character - CHAR_OFFSET_FOR_DIGIT;
+ } else if (Character.isUpperCase(character)) {
+ return character - CHAR_OFFSET_FOR_UPPERCASE;
+ } else {
+ throw new NumberFormatException("invalid character:" + character);
}
- return Character.isDigit(c) ? c - '0' : c - 'A' + 10;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/AnytoAny.java b/src/main/java/com/thealgorithms/conversions/AnytoAny.java
index 052d6dba6953..e7bdbc2b79c4 100644
--- a/src/main/java/com/thealgorithms/conversions/AnytoAny.java
+++ b/src/main/java/com/thealgorithms/conversions/AnytoAny.java
@@ -1,31 +1,68 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
+/**
+ * A utility class for converting numbers from any base to any other base.
+ *
+ * This class provides a method to convert a source number from a given base
+ * to a destination number in another base. Valid bases range from 2 to 10.
+ */
+public final class AnytoAny {
+ private AnytoAny() {
+ }
+
+ /**
+ * Converts a number from a source base to a destination base.
+ *
+ * @param sourceNumber The number in the source base (as an integer).
+ * @param sourceBase The base of the source number (between 2 and 10).
+ * @param destBase The base to which the number should be converted (between 2 and 10).
+ * @throws IllegalArgumentException if the bases are not between 2 and 10.
+ * @return The converted number in the destination base (as an integer).
+ */
+ public static int convertBase(int sourceNumber, int sourceBase, int destBase) {
+ if (sourceBase < 2 || sourceBase > 10 || destBase < 2 || destBase > 10) {
+ throw new IllegalArgumentException("Bases must be between 2 and 10.");
+ }
-// given a source number , source base, destination base, this code can give you the destination
-// number.
-// sn ,sb,db ---> ()dn . this is what we have to do .
+ int decimalValue = toDecimal(sourceNumber, sourceBase);
+ return fromDecimal(decimalValue, destBase);
+ }
-public class AnytoAny {
+ /**
+ * Converts a number from a given base to its decimal representation (base 10).
+ *
+ * @param number The number in the original base.
+ * @param base The base of the given number.
+ * @return The decimal representation of the number.
+ */
+ private static int toDecimal(int number, int base) {
+ int decimalValue = 0;
+ int multiplier = 1;
- public static void main(String[] args) {
- Scanner scn = new Scanner(System.in);
- int sn = scn.nextInt();
- int sb = scn.nextInt();
- int db = scn.nextInt();
- int m = 1, dec = 0, dn = 0;
- while (sn != 0) {
- dec = dec + (sn % 10) * m;
- m *= sb;
- sn /= 10;
+ while (number != 0) {
+ decimalValue += (number % 10) * multiplier;
+ multiplier *= base;
+ number /= 10;
}
- m = 1;
- while (dec != 0) {
- dn = dn + (dec % db) * m;
- m *= 10;
- dec /= db;
+ return decimalValue;
+ }
+
+ /**
+ * Converts a decimal (base 10) number to a specified base.
+ *
+ * @param decimal The decimal number to convert.
+ * @param base The destination base for conversion.
+ * @return The number in the specified base.
+ */
+ private static int fromDecimal(int decimal, int base) {
+ int result = 0;
+ int multiplier = 1;
+
+ while (decimal != 0) {
+ result += (decimal % base) * multiplier;
+ multiplier *= 10;
+ decimal /= base;
}
- System.out.println(dn);
- scn.close();
+ return result;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/BinaryToDecimal.java b/src/main/java/com/thealgorithms/conversions/BinaryToDecimal.java
index fdf9df7b2467..36c0790e565f 100644
--- a/src/main/java/com/thealgorithms/conversions/BinaryToDecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/BinaryToDecimal.java
@@ -1,32 +1,33 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
* This class converts a Binary number to a Decimal number
*/
-class BinaryToDecimal {
+final class BinaryToDecimal {
+ private static final int BINARY_BASE = 2;
- public static long binaryToDecimal(long binNum) {
- long binCopy, d, s = 0, power = 0;
- binCopy = binNum;
- while (binCopy != 0) {
- d = binCopy % 10;
- s += d * (long) Math.pow(2, power++);
- binCopy /= 10;
- }
- return s;
+ private BinaryToDecimal() {
}
/**
- * Main Method
+ * Converts a binary number to its decimal equivalent.
*
- * @param args Command line arguments
+ * @param binaryNumber The binary number to convert.
+ * @return The decimal equivalent of the binary number.
+ * @throws IllegalArgumentException If the binary number contains digits other than 0 and 1.
*/
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- System.out.print("Binary number: ");
- System.out.println("Decimal equivalent:" + binaryToDecimal(sc.nextLong()));
- sc.close();
+ public static long binaryToDecimal(long binaryNumber) {
+ long decimalValue = 0;
+ long power = 0;
+
+ while (binaryNumber != 0) {
+ long digit = binaryNumber % 10;
+ if (digit > 1) {
+ throw new IllegalArgumentException("Incorrect binary digit: " + digit);
+ }
+ decimalValue += (long) (digit * Math.pow(BINARY_BASE, power++));
+ binaryNumber /= 10;
+ }
+ return decimalValue;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/BinaryToHexadecimal.java b/src/main/java/com/thealgorithms/conversions/BinaryToHexadecimal.java
index c942cbb7d843..9ff2f593fe1f 100644
--- a/src/main/java/com/thealgorithms/conversions/BinaryToHexadecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/BinaryToHexadecimal.java
@@ -1,57 +1,63 @@
package com.thealgorithms.conversions;
-import java.util.*;
+import java.util.HashMap;
+import java.util.Map;
/**
* Converts any Binary Number to a Hexadecimal Number
*
* @author Nishita Aggarwal
*/
-public class BinaryToHexadecimal {
+public final class BinaryToHexadecimal {
+ private static final int BITS_IN_HEX_DIGIT = 4;
+ private static final int BASE_BINARY = 2;
+ private static final int BASE_DECIMAL = 10;
+ private static final int HEX_START_DECIMAL = 10;
+ private static final int HEX_END_DECIMAL = 15;
+
+ private BinaryToHexadecimal() {
+ }
/**
- * This method converts a binary number to a hexadecimal number.
+ * Converts a binary number to a hexadecimal number.
*
- * @param binary The binary number
- * @return The hexadecimal number
+ * @param binary The binary number to convert.
+ * @return The hexadecimal representation of the binary number.
+ * @throws IllegalArgumentException If the binary number contains digits other than 0 and 1.
*/
- static String binToHex(int binary) {
- // hm to store hexadecimal codes for binary numbers within the range: 0000 to 1111 i.e. for
- // decimal numbers 0 to 15
- HashMap hm = new HashMap<>();
- // String to store hexadecimal code
- String hex = "";
- int i;
- for (i = 0; i < 10; i++) {
- hm.put(i, String.valueOf(i));
- }
- for (i = 10; i < 16; i++) {
- hm.put(i, String.valueOf((char) ('A' + i - 10)));
- }
- int currbit;
+ public static String binToHex(int binary) {
+ Map hexMap = initializeHexMap();
+ StringBuilder hex = new StringBuilder();
+
while (binary != 0) {
- int code4 = 0; // to store decimal equivalent of number formed by 4 decimal digits
- for (i = 0; i < 4; i++) {
- currbit = binary % 10;
- binary = binary / 10;
- code4 += currbit * Math.pow(2, i);
+ int decimalValue = 0;
+ for (int i = 0; i < BITS_IN_HEX_DIGIT; i++) {
+ int currentBit = binary % BASE_DECIMAL;
+ if (currentBit > 1) {
+ throw new IllegalArgumentException("Incorrect binary digit: " + currentBit);
+ }
+ binary /= BASE_DECIMAL;
+ decimalValue += (int) (currentBit * Math.pow(BASE_BINARY, i));
}
- hex = hm.get(code4) + hex;
+ hex.insert(0, hexMap.get(decimalValue));
}
- return hex;
+
+ return !hex.isEmpty() ? hex.toString() : "0";
}
/**
- * Main method
+ * Initializes the hexadecimal map with decimal to hexadecimal mappings.
*
- * @param args Command line arguments
+ * @return The initialized map containing mappings from decimal numbers to hexadecimal digits.
*/
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- System.out.println("Enter binary number:");
- int binary = sc.nextInt();
- String hex = binToHex(binary);
- System.out.println("Hexadecimal Code:" + hex);
- sc.close();
+ private static Map initializeHexMap() {
+ Map hexMap = new HashMap<>();
+ for (int i = 0; i < BASE_DECIMAL; i++) {
+ hexMap.put(i, String.valueOf(i));
+ }
+ for (int i = HEX_START_DECIMAL; i <= HEX_END_DECIMAL; i++) {
+ hexMap.put(i, String.valueOf((char) ('A' + i - HEX_START_DECIMAL)));
+ }
+ return hexMap;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/BinaryToOctal.java b/src/main/java/com/thealgorithms/conversions/BinaryToOctal.java
index 70bad812141b..5407c8525a23 100644
--- a/src/main/java/com/thealgorithms/conversions/BinaryToOctal.java
+++ b/src/main/java/com/thealgorithms/conversions/BinaryToOctal.java
@@ -1,25 +1,11 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
+public final class BinaryToOctal {
+ private static final int BITS_PER_OCTAL_DIGIT = 3;
+ private static final int BINARY_BASE = 2;
+ private static final int DECIMAL_BASE = 10;
-/**
- * Converts any Binary number to an Octal Number
- *
- * @author Zachary Jones
- */
-public class BinaryToOctal {
-
- /**
- * Main method
- *
- * @param args Command line arguments
- */
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- System.out.println("Input the binary number: ");
- int b = sc.nextInt();
- System.out.println("Octal equivalent: " + convertBinaryToOctal(b));
- sc.close();
+ private BinaryToOctal() {
}
/**
@@ -27,21 +13,33 @@ public static void main(String[] args) {
*
* @param binary The binary number
* @return The octal number
+ * @throws IllegalArgumentException if the input is not a valid binary number
*/
public static String convertBinaryToOctal(int binary) {
- String octal = "";
- int currBit = 0, j = 1;
+ if (binary == 0) {
+ return "0";
+ }
+
+ if (!String.valueOf(binary).matches("[01]+")) {
+ throw new IllegalArgumentException("Input is not a valid binary number.");
+ }
+
+ StringBuilder octal = new StringBuilder();
+ int currentBit;
+ int bitValueMultiplier = 1;
+
while (binary != 0) {
- int code3 = 0;
- for (int i = 0; i < 3; i++) {
- currBit = binary % 10;
- binary = binary / 10;
- code3 += currBit * j;
- j *= 2;
+ int octalDigit = 0;
+ for (int i = 0; i < BITS_PER_OCTAL_DIGIT && binary != 0; i++) {
+ currentBit = binary % DECIMAL_BASE;
+ binary /= DECIMAL_BASE;
+ octalDigit += currentBit * bitValueMultiplier;
+ bitValueMultiplier *= BINARY_BASE;
}
- octal = code3 + octal;
- j = 1;
+ octal.insert(0, octalDigit);
+ bitValueMultiplier = 1; // Reset multiplier for the next group
}
- return octal;
+
+ return octal.toString();
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/DecimalToAnyBase.java b/src/main/java/com/thealgorithms/conversions/DecimalToAnyBase.java
index 31ef2bffb708..a5615dc002f5 100644
--- a/src/main/java/com/thealgorithms/conversions/DecimalToAnyBase.java
+++ b/src/main/java/com/thealgorithms/conversions/DecimalToAnyBase.java
@@ -1,67 +1,69 @@
package com.thealgorithms.conversions;
-import java.io.BufferedReader;
-import java.io.InputStreamReader;
import java.util.ArrayList;
+import java.util.List;
/**
- * @author Varun Upadhyay (https://github.com/varunu28)
+ * Class that provides methods to convert a decimal number to a string representation
+ * in any specified base between 2 and 36.
+ *
+ * @author Varun Upadhyay (...)
*/
-// Driver Program
-public class DecimalToAnyBase {
+public final class DecimalToAnyBase {
+ private static final int MIN_BASE = 2;
+ private static final int MAX_BASE = 36;
+ private static final char ZERO_CHAR = '0';
+ private static final char A_CHAR = 'A';
+ private static final int DIGIT_OFFSET = 10;
- public static void main(String[] args) throws Exception {
- BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
- System.out.println("Enter the decimal input below: ");
- int decInput = Integer.parseInt(br.readLine());
- System.out.println();
-
- System.out.println("Enter the base below: ");
- int base = Integer.parseInt(br.readLine());
- System.out.println();
-
- System.out.println("Decimal Input"
- + " is: " + decInput);
- System.out.println("Value of " + decInput + " in base " + base + " is: " + convertToAnyBase(decInput, base));
-
- br.close();
+ private DecimalToAnyBase() {
}
/**
- * This method produces a String value of any given input decimal in any
- * base
+ * Converts a decimal number to a string representation in the specified base.
+ * For example, converting the decimal number 10 to base 2 would return "1010".
*
- * @param inp Decimal of which we need the value in base in String format
- * @return string format of the converted value in the given base
+ * @param decimal the decimal number to convert
+ * @param base the base to convert to (must be between {@value #MIN_BASE} and {@value #MAX_BASE})
+ * @return the string representation of the number in the specified base
+ * @throws IllegalArgumentException if the base is out of the supported range
*/
- public static String convertToAnyBase(int inp, int base) {
- ArrayList charArr = new ArrayList<>();
+ public static String convertToAnyBase(int decimal, int base) {
+ if (base < MIN_BASE || base > MAX_BASE) {
+ throw new IllegalArgumentException("Base must be between " + MIN_BASE + " and " + MAX_BASE);
+ }
- while (inp > 0) {
- charArr.add(reVal(inp % base));
- inp /= base;
+ if (decimal == 0) {
+ return String.valueOf(ZERO_CHAR);
}
- StringBuilder str = new StringBuilder(charArr.size());
+ List digits = new ArrayList<>();
+ while (decimal > 0) {
+ digits.add(convertToChar(decimal % base));
+ decimal /= base;
+ }
- for (Character ch : charArr) {
- str.append(ch);
+ StringBuilder result = new StringBuilder(digits.size());
+ for (int i = digits.size() - 1; i >= 0; i--) {
+ result.append(digits.get(i));
}
- return str.reverse().toString();
+ return result.toString();
}
/**
- * This method produces character value of the input integer and returns it
+ * Converts an integer value to its corresponding character in the specified base.
+ * This method is used to convert values from 0 to 35 into their appropriate character representation.
+ * For example, 0-9 are represented as '0'-'9', and 10-35 are represented as 'A'-'Z'.
*
- * @param num integer of which we need the character value of
- * @return character value of input integer
+ * @param value the integer value to convert (should be less than the base value)
+ * @return the character representing the value in the specified base
*/
- public static char reVal(int num) {
- if (num >= 0 && num <= 9) {
- return (char) (num + '0');
+ private static char convertToChar(int value) {
+ if (value >= 0 && value <= 9) {
+ return (char) (ZERO_CHAR + value);
} else {
- return (char) (num - 10 + 'A');
+ return (char) (A_CHAR + value - DIGIT_OFFSET);
}
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/DecimalToBinary.java b/src/main/java/com/thealgorithms/conversions/DecimalToBinary.java
index a6119cfbc9bc..e8d033e0093c 100644
--- a/src/main/java/com/thealgorithms/conversions/DecimalToBinary.java
+++ b/src/main/java/com/thealgorithms/conversions/DecimalToBinary.java
@@ -1,55 +1,49 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
- * This class converts a Decimal number to a Binary number
+ * This class provides methods to convert a decimal number to a binary number.
*/
-class DecimalToBinary {
+final class DecimalToBinary {
+ private static final int BINARY_BASE = 2;
+ private static final int DECIMAL_MULTIPLIER = 10;
- /**
- * Main Method
- *
- * @param args Command Line Arguments
- */
- public static void main(String[] args) {
- conventionalConversion();
- bitwiseConversion();
+ private DecimalToBinary() {
}
/**
- * This method converts a decimal number to a binary number using a
- * conventional algorithm.
+ * Converts a decimal number to a binary number using a conventional algorithm.
+ * @param decimalNumber the decimal number to convert
+ * @return the binary representation of the decimal number
*/
- public static void conventionalConversion() {
- int n, b = 0, c = 0, d;
- Scanner input = new Scanner(System.in);
- System.out.printf("Conventional conversion.%n Enter the decimal number: ");
- n = input.nextInt();
- while (n != 0) {
- d = n % 2;
- b = b + d * (int) Math.pow(10, c++);
- n /= 2;
- } // converting decimal to binary
- System.out.println("\tBinary number: " + b);
- input.close();
+ public static int convertUsingConventionalAlgorithm(int decimalNumber) {
+ int binaryNumber = 0;
+ int position = 1;
+
+ while (decimalNumber > 0) {
+ int remainder = decimalNumber % BINARY_BASE;
+ binaryNumber += remainder * position;
+ position *= DECIMAL_MULTIPLIER;
+ decimalNumber /= BINARY_BASE;
+ }
+
+ return binaryNumber;
}
/**
- * This method converts a decimal number to a binary number using a bitwise
- * algorithm
+ * Converts a decimal number to a binary number using a bitwise algorithm.
+ * @param decimalNumber the decimal number to convert
+ * @return the binary representation of the decimal number
*/
- public static void bitwiseConversion() {
- int n, b = 0, c = 0, d;
- Scanner input = new Scanner(System.in);
- System.out.printf("Bitwise conversion.%n Enter the decimal number: ");
- n = input.nextInt();
- while (n != 0) {
- d = (n & 1);
- b += d * (int) Math.pow(10, c++);
- n >>= 1;
+ public static int convertUsingBitwiseAlgorithm(int decimalNumber) {
+ int binaryNumber = 0;
+ int position = 1;
+
+ while (decimalNumber > 0) {
+ int leastSignificantBit = decimalNumber & 1;
+ binaryNumber += leastSignificantBit * position;
+ position *= DECIMAL_MULTIPLIER;
+ decimalNumber >>= 1;
}
- System.out.println("\tBinary number: " + b);
- input.close();
+ return binaryNumber;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/DecimalToHexaDecimal.java b/src/main/java/com/thealgorithms/conversions/DecimalToHexaDecimal.java
deleted file mode 100644
index 3564acbe568c..000000000000
--- a/src/main/java/com/thealgorithms/conversions/DecimalToHexaDecimal.java
+++ /dev/null
@@ -1,49 +0,0 @@
-package com.thealgorithms.conversions;
-
-// hex = [0 - 9] -> [A - F]
-class DecimalToHexaDecimal {
-
- private static final int sizeOfIntInHalfBytes = 8;
- private static final int numberOfBitsInAHalfByte = 4;
- private static final int halfByte = 0x0F;
- private static final char[] hexDigits = {
- '0',
- '1',
- '2',
- '3',
- '4',
- '5',
- '6',
- '7',
- '8',
- '9',
- 'A',
- 'B',
- 'C',
- 'D',
- 'E',
- 'F',
- };
-
- // Returns the hex value of the dec entered in the parameter.
- public static String decToHex(int dec) {
- StringBuilder hexBuilder = new StringBuilder(sizeOfIntInHalfBytes);
- hexBuilder.setLength(sizeOfIntInHalfBytes);
- for (int i = sizeOfIntInHalfBytes - 1; i >= 0; --i) {
- int j = dec & halfByte;
- hexBuilder.setCharAt(i, hexDigits[j]);
- dec >>= numberOfBitsInAHalfByte;
- }
- return hexBuilder.toString().toLowerCase();
- }
-
- // Test above function.
- public static void main(String[] args) {
- System.out.println("Test...");
- int dec = 305445566;
- String libraryDecToHex = Integer.toHexString(dec);
- String decToHex = decToHex(dec);
- System.out.println("Result from the library : " + libraryDecToHex);
- System.out.println("Result decToHex method : " + decToHex);
- }
-}
diff --git a/src/main/java/com/thealgorithms/conversions/DecimalToHexadecimal.java b/src/main/java/com/thealgorithms/conversions/DecimalToHexadecimal.java
new file mode 100644
index 000000000000..47a1e36b27e3
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/DecimalToHexadecimal.java
@@ -0,0 +1,42 @@
+package com.thealgorithms.conversions;
+
+/**
+ * This class provides a method to convert a decimal number to a hexadecimal string.
+ */
+final class DecimalToHexadecimal {
+ private static final int SIZE_OF_INT_IN_HALF_BYTES = 8;
+ private static final int NUMBER_OF_BITS_IN_HALF_BYTE = 4;
+ private static final int HALF_BYTE_MASK = 0x0F;
+ private static final char[] HEX_DIGITS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
+
+ private DecimalToHexadecimal() {
+ }
+
+ /**
+ * Converts a decimal number to a hexadecimal string.
+ * @param decimal the decimal number to convert
+ * @return the hexadecimal representation of the decimal number
+ */
+ public static String decToHex(int decimal) {
+ StringBuilder hexBuilder = new StringBuilder(SIZE_OF_INT_IN_HALF_BYTES);
+ for (int i = SIZE_OF_INT_IN_HALF_BYTES - 1; i >= 0; --i) {
+ int currentHalfByte = decimal & HALF_BYTE_MASK;
+ hexBuilder.insert(0, HEX_DIGITS[currentHalfByte]);
+ decimal >>= NUMBER_OF_BITS_IN_HALF_BYTE;
+ }
+ return removeLeadingZeros(hexBuilder.toString().toLowerCase());
+ }
+
+ private static String removeLeadingZeros(String str) {
+ if (str == null || str.isEmpty()) {
+ return str;
+ }
+
+ int i = 0;
+ while (i < str.length() && str.charAt(i) == '0') {
+ i++;
+ }
+
+ return i == str.length() ? "0" : str.substring(i);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/DecimalToOctal.java b/src/main/java/com/thealgorithms/conversions/DecimalToOctal.java
index 0f72f462c753..75687fc589ae 100644
--- a/src/main/java/com/thealgorithms/conversions/DecimalToOctal.java
+++ b/src/main/java/com/thealgorithms/conversions/DecimalToOctal.java
@@ -1,32 +1,38 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
* This class converts Decimal numbers to Octal Numbers
*/
-public class DecimalToOctal {
+public final class DecimalToOctal {
+ private static final int OCTAL_BASE = 8;
+ private static final int INITIAL_OCTAL_VALUE = 0;
+ private static final int INITIAL_PLACE_VALUE = 1;
+
+ private DecimalToOctal() {
+ }
/**
- * Main Method
+ * Converts a decimal number to its octal equivalent.
*
- * @param args Command line Arguments
+ * @param decimal The decimal number to convert.
+ * @return The octal equivalent as an integer.
+ * @throws IllegalArgumentException if the decimal number is negative.
*/
+ public static int convertToOctal(int decimal) {
+ if (decimal < 0) {
+ throw new IllegalArgumentException("Decimal number cannot be negative.");
+ }
+
+ int octal = INITIAL_OCTAL_VALUE;
+ int placeValue = INITIAL_PLACE_VALUE;
- // enter in a decimal value to get Octal output
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- int n, k, d, s = 0, c = 0;
- System.out.print("Decimal number: ");
- n = sc.nextInt();
- k = n;
- while (k != 0) {
- d = k % 8;
- s += d * (int) Math.pow(10, c++);
- k /= 8;
+ while (decimal != 0) {
+ int remainder = decimal % OCTAL_BASE;
+ octal += remainder * placeValue;
+ decimal /= OCTAL_BASE;
+ placeValue *= 10;
}
- System.out.println("Octal equivalent:" + s);
- sc.close();
+ return octal;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/EndianConverter.java b/src/main/java/com/thealgorithms/conversions/EndianConverter.java
new file mode 100644
index 000000000000..0d69098e8255
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/EndianConverter.java
@@ -0,0 +1,47 @@
+package com.thealgorithms.conversions;
+
+/**
+ * Utility class for converting integers between big-endian and little-endian formats.
+ *
+ * Endianness defines how byte sequences represent multi-byte data types:
+ *
+ *
Big-endian: The most significant byte (MSB) comes first.
+ *
Little-endian: The least significant byte (LSB) comes first.
+ *
+ *
+ * Example conversion:
+ *
+ *
Big-endian to little-endian: {@code 0x12345678} → {@code 0x78563412}
+ *
Little-endian to big-endian: {@code 0x78563412} → {@code 0x12345678}
+ *
+ *
+ *
Note: Both conversions in this utility are equivalent since reversing the bytes is symmetric.
+ *
+ *
This class only supports 32-bit integers.
+ *
+ * @author Hardvan
+ */
+public final class EndianConverter {
+ private EndianConverter() {
+ }
+
+ /**
+ * Converts a 32-bit integer from big-endian to little-endian.
+ *
+ * @param value the integer in big-endian format
+ * @return the integer in little-endian format
+ */
+ public static int bigToLittleEndian(int value) {
+ return Integer.reverseBytes(value);
+ }
+
+ /**
+ * Converts a 32-bit integer from little-endian to big-endian.
+ *
+ * @param value the integer in little-endian format
+ * @return the integer in big-endian format
+ */
+ public static int littleToBigEndian(int value) {
+ return Integer.reverseBytes(value);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/HexToOct.java b/src/main/java/com/thealgorithms/conversions/HexToOct.java
index 2a57fbde5c41..d3a672d37424 100644
--- a/src/main/java/com/thealgorithms/conversions/HexToOct.java
+++ b/src/main/java/com/thealgorithms/conversions/HexToOct.java
@@ -1,72 +1,62 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
* Converts any Hexadecimal Number to Octal
*
* @author Tanmay Joshi
*/
-public class HexToOct {
+public final class HexToOct {
+ private HexToOct() {
+ }
/**
- * This method converts a Hexadecimal number to a decimal number
+ * Converts a Hexadecimal number to a Decimal number.
*
- * @param s The Hexadecimal Number
- * @return The Decimal number
+ * @param hex The Hexadecimal number as a String.
+ * @return The Decimal equivalent as an integer.
*/
- public static int hex2decimal(String s) {
- String str = "0123456789ABCDEF";
- s = s.toUpperCase();
- int val = 0;
- for (int i = 0; i < s.length(); i++) {
- char a = s.charAt(i);
- int n = str.indexOf(a);
- val = 16 * val + n;
+ public static int hexToDecimal(String hex) {
+ String hexDigits = "0123456789ABCDEF";
+ hex = hex.toUpperCase();
+ int decimalValue = 0;
+
+ for (int i = 0; i < hex.length(); i++) {
+ char hexChar = hex.charAt(i);
+ int digitValue = hexDigits.indexOf(hexChar);
+ decimalValue = 16 * decimalValue + digitValue;
}
- return val;
+
+ return decimalValue;
}
/**
- * This method converts a Decimal number to a octal number
+ * Converts a Decimal number to an Octal number.
*
- * @param q The Decimal Number
- * @return The Octal number
+ * @param decimal The Decimal number as an integer.
+ * @return The Octal equivalent as an integer.
*/
- public static int decimal2octal(int q) {
- int now;
- int i = 1;
- int octnum = 0;
- while (q > 0) {
- now = q % 8;
- octnum = (now * (int) (Math.pow(10, i))) + octnum;
- q /= 8;
- i++;
+ public static int decimalToOctal(int decimal) {
+ int octalValue = 0;
+ int placeValue = 1;
+
+ while (decimal > 0) {
+ int remainder = decimal % 8;
+ octalValue += remainder * placeValue;
+ decimal /= 8;
+ placeValue *= 10;
}
- octnum /= 10;
- return octnum;
+
+ return octalValue;
}
/**
- * Main method that gets the hex input from user and converts it into octal.
+ * Converts a Hexadecimal number to an Octal number.
*
- * @param args arguments
+ * @param hex The Hexadecimal number as a String.
+ * @return The Octal equivalent as an integer.
*/
- public static void main(String[] args) {
- String hexadecnum;
- int decnum, octalnum;
- Scanner scan = new Scanner(System.in);
-
- System.out.print("Enter Hexadecimal Number : ");
- hexadecnum = scan.nextLine();
-
- // first convert hexadecimal to decimal
- decnum = hex2decimal(hexadecnum); // Pass the string to the hex2decimal function and get the decimal form in
- // variable decnum
-
- // convert decimal to octal
- octalnum = decimal2octal(decnum);
- System.out.println("Number in octal: " + octalnum);
- scan.close();
+ public static int hexToOctal(String hex) {
+ int decimalValue = hexToDecimal(hex);
+ return decimalToOctal(decimalValue);
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java b/src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java
index 5372c95f23d4..c0eb9a01ba17 100644
--- a/src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java
+++ b/src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java
@@ -1,45 +1,62 @@
package com.thealgorithms.conversions;
-// Hex [0-9],[A-F] -> Binary [0,1]
+/**
+ * Utility class for converting hexadecimal numbers to binary representation.
+ *
+ * A hexadecimal number consists of digits from {@code [0-9]} and {@code [A-F]} (case-insensitive),
+ * while binary representation uses only {@code [0, 1]}.
+ *
+ * This class provides methods to:
+ *
+ *
Convert a hexadecimal string to its binary string equivalent.
+ *
Ensure the binary output is padded to 8 bits (1 byte).
+ *
+ *
+ * Example:
+ *
+ *
{@code "A1"} → {@code "10100001"}
+ *
{@code "1"} → {@code "00000001"}
+ *
+ *
+ *
This class assumes that the input hexadecimal string is valid.
+ */
public class HexaDecimalToBinary {
- private final int LONG_BITS = 8;
-
+ /**
+ * Converts a hexadecimal string to its binary string equivalent.
+ * The binary output is padded to a minimum of 8 bits (1 byte).
+ * Steps:
+ *
+ *
Convert the hexadecimal string to an integer.
+ *
Convert the integer to a binary string.
+ *
Pad the binary string to ensure it is at least 8 bits long.
+ *
Return the padded binary string.
+ *
+ *
+ * @param numHex the hexadecimal string (e.g., "A1", "7F")
+ * @throws NumberFormatException if the input string is not a valid hexadecimal number
+ * @return the binary string representation, padded to 8 bits (e.g., "10100001")
+ */
public String convert(String numHex) {
- // String a HexaDecimal:
int conHex = Integer.parseInt(numHex, 16);
- // Hex a Binary:
String binary = Integer.toBinaryString(conHex);
- // Output:
return completeDigits(binary);
}
+ /**
+ * Pads the binary string to ensure it is at least 8 bits long.
+ * If the binary string is shorter than 8 bits, it adds leading zeros.
+ *
+ * @param binNum the binary string to pad
+ * @return the padded binary string with a minimum length of 8
+ */
public String completeDigits(String binNum) {
- for (int i = binNum.length(); i < LONG_BITS; i++) {
- binNum = "0" + binNum;
+ final int byteSize = 8;
+ StringBuilder binNumBuilder = new StringBuilder(binNum);
+ while (binNumBuilder.length() < byteSize) {
+ binNumBuilder.insert(0, "0");
}
+ binNum = binNumBuilder.toString();
return binNum;
}
-
- public static void main(String[] args) {
- // Testing Numbers:
- String[] hexNums = {
- "1",
- "A1",
- "ef",
- "BA",
- "AA",
- "BB",
- "19",
- "01",
- "02",
- "03",
- "04",
- };
- HexaDecimalToBinary objConvert = new HexaDecimalToBinary();
-
- for (String num : hexNums) {
- System.out.println(num + " = " + objConvert.convert(num));
- }
- }
}
diff --git a/src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java b/src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java
index 7675c83ebcfa..2cf6024d90a3 100644
--- a/src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java
@@ -1,37 +1,45 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
-public class HexaDecimalToDecimal {
+/**
+ * Utility class for converting a hexadecimal string to its decimal representation.
+ *
+ * A hexadecimal number uses the base-16 numeral system, with the following characters:
+ *
+ *
Digits: 0-9
+ *
Letters: A-F (case-insensitive)
+ *
+ * Each character represents a power of 16. For example:
+ *
This class provides a method to perform the conversion without using built-in Java utilities.
+ */
+public final class HexaDecimalToDecimal {
+ private HexaDecimalToDecimal() {
+ }
- // convert hexadecimal to decimal
+ /**
+ * Converts a hexadecimal string to its decimal integer equivalent.
+ *
The input string is case-insensitive, and must contain valid hexadecimal characters [0-9, A-F].
+ *
+ * @param hex the hexadecimal string to convert
+ * @return the decimal integer representation of the input hexadecimal string
+ * @throws IllegalArgumentException if the input string contains invalid characters
+ */
public static int getHexaToDec(String hex) {
String digits = "0123456789ABCDEF";
hex = hex.toUpperCase();
int val = 0;
+
for (int i = 0; i < hex.length(); i++) {
int d = digits.indexOf(hex.charAt(i));
+ if (d == -1) {
+ throw new IllegalArgumentException("Invalid hexadecimal character: " + hex.charAt(i));
+ }
val = 16 * val + d;
}
- return val;
- }
-
- // Main method gets the hexadecimal input from user and converts it into Decimal output.
- public static void main(String[] args) {
- String hexa_Input;
- int dec_output;
- Scanner scan = new Scanner(System.in);
- System.out.print("Enter Hexadecimal Number : ");
- hexa_Input = scan.nextLine();
-
- // convert hexadecimal to decimal
- dec_output = getHexaToDec(hexa_Input);
- /*
- Pass the string to the getHexaToDec function
- and it returns the decimal form in the variable dec_output.
- */
- System.out.println("Number in Decimal: " + dec_output);
- scan.close();
+ return val;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/IPConverter.java b/src/main/java/com/thealgorithms/conversions/IPConverter.java
new file mode 100644
index 000000000000..765cb0201dd5
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/IPConverter.java
@@ -0,0 +1,58 @@
+package com.thealgorithms.conversions;
+
+/**
+ * Converts an IPv4 address to its binary equivalent and vice-versa.
+ * IP to Binary: Converts an IPv4 address to its binary equivalent.
+ * Example: 127.3.4.5 -> 01111111.00000011.00000100.00000101
+ *
+ * Binary to IP: Converts a binary equivalent to an IPv4 address.
+ * Example: 01111111.00000011.00000100.00000101 -> 127.3.4.5
+ *
+ * @author Hardvan
+ */
+public final class IPConverter {
+ private IPConverter() {
+ }
+
+ /**
+ * Converts an IPv4 address to its binary equivalent.
+ * @param ip The IPv4 address to convert.
+ * @return The binary equivalent of the IPv4 address.
+ */
+ public static String ipToBinary(String ip) {
+ StringBuilder binary = new StringBuilder();
+ for (String octet : ip.split("\\.")) {
+ binary.append(octetToBinary(Integer.parseInt(octet))).append(".");
+ }
+ return binary.substring(0, binary.length() - 1);
+ }
+
+ /**
+ * Converts a single octet to its 8-bit binary representation.
+ * @param octet The octet to convert (0-255).
+ * @return The 8-bit binary representation as a String.
+ */
+ private static String octetToBinary(int octet) {
+ char[] binary = {'0', '0', '0', '0', '0', '0', '0', '0'};
+ for (int i = 7; i >= 0; i--) {
+ if ((octet & 1) == 1) {
+ binary[i] = '1';
+ }
+ octet >>>= 1;
+ }
+ return new String(binary);
+ }
+
+ /**
+ * Converts a binary equivalent to an IPv4 address.
+ * @param binary The binary equivalent to convert.
+ * @return The IPv4 address of the binary equivalent.
+ */
+ public static String binaryToIP(String binary) {
+ StringBuilder ip = new StringBuilder();
+ for (String octet : binary.split("\\.")) {
+ ip.append(Integer.parseInt(octet, 2)).append(".");
+ }
+ return ip.substring(0, ip.length() - 1);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/IPv6Converter.java b/src/main/java/com/thealgorithms/conversions/IPv6Converter.java
new file mode 100644
index 000000000000..d42ffd027514
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/IPv6Converter.java
@@ -0,0 +1,98 @@
+package com.thealgorithms.conversions;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.Arrays;
+
+/**
+ * A utility class for converting between IPv6 and IPv4 addresses.
+ *
+ * - Converts IPv4 to IPv6-mapped IPv6 address.
+ * - Extracts IPv4 address from IPv6-mapped IPv6.
+ * - Handles exceptions for invalid inputs.
+ *
+ * @author Hardvan
+ */
+public final class IPv6Converter {
+ private IPv6Converter() {
+ }
+
+ /**
+ * Converts an IPv4 address (e.g., "192.0.2.128") to an IPv6-mapped IPv6 address.
+ * Example: IPv4 "192.0.2.128" -> IPv6 "::ffff:192.0.2.128"
+ *
+ * @param ipv4Address The IPv4 address in string format.
+ * @return The corresponding IPv6-mapped IPv6 address.
+ * @throws UnknownHostException If the IPv4 address is invalid.
+ * @throws IllegalArgumentException If the IPv6 address is not a mapped IPv4 address.
+ */
+ public static String ipv4ToIpv6(String ipv4Address) throws UnknownHostException {
+ if (ipv4Address == null || ipv4Address.isEmpty()) {
+ throw new UnknownHostException("IPv4 address is empty.");
+ }
+
+ InetAddress ipv4 = InetAddress.getByName(ipv4Address);
+ byte[] ipv4Bytes = ipv4.getAddress();
+
+ // Create IPv6-mapped IPv6 address (starts with ::ffff:)
+ byte[] ipv6Bytes = new byte[16];
+ ipv6Bytes[10] = (byte) 0xff;
+ ipv6Bytes[11] = (byte) 0xff;
+ System.arraycopy(ipv4Bytes, 0, ipv6Bytes, 12, 4);
+
+ // Manually format to "::ffff:x.x.x.x" format
+ StringBuilder ipv6String = new StringBuilder("::ffff:");
+ for (int i = 12; i < 16; i++) {
+ ipv6String.append(ipv6Bytes[i] & 0xFF);
+ if (i < 15) {
+ ipv6String.append('.');
+ }
+ }
+ return ipv6String.toString();
+ }
+
+ /**
+ * Extracts the IPv4 address from an IPv6-mapped IPv6 address.
+ * Example: IPv6 "::ffff:192.0.2.128" -> IPv4 "192.0.2.128"
+ *
+ * @param ipv6Address The IPv6 address in string format.
+ * @return The extracted IPv4 address.
+ * @throws UnknownHostException If the IPv6 address is invalid or not a mapped IPv4 address.
+ */
+ public static String ipv6ToIpv4(String ipv6Address) throws UnknownHostException {
+ InetAddress ipv6 = InetAddress.getByName(ipv6Address);
+ byte[] ipv6Bytes = ipv6.getAddress();
+
+ // Check if the address is an IPv6-mapped IPv4 address
+ if (isValidIpv6MappedIpv4(ipv6Bytes)) {
+ byte[] ipv4Bytes = Arrays.copyOfRange(ipv6Bytes, 12, 16);
+ InetAddress ipv4 = InetAddress.getByAddress(ipv4Bytes);
+ return ipv4.getHostAddress();
+ } else {
+ throw new IllegalArgumentException("Not a valid IPv6-mapped IPv4 address.");
+ }
+ }
+
+ /**
+ * Helper function to check if the given byte array represents
+ * an IPv6-mapped IPv4 address (prefix 0:0:0:0:0:ffff).
+ *
+ * @param ipv6Bytes Byte array representation of the IPv6 address.
+ * @return True if the address is IPv6-mapped IPv4, otherwise false.
+ */
+ private static boolean isValidIpv6MappedIpv4(byte[] ipv6Bytes) {
+ // IPv6-mapped IPv4 addresses are 16 bytes long, with the first 10 bytes set to 0,
+ // followed by 0xff, 0xff, and the last 4 bytes representing the IPv4 address.
+ if (ipv6Bytes.length != 16) {
+ return false;
+ }
+
+ for (int i = 0; i < 10; i++) {
+ if (ipv6Bytes[i] != 0) {
+ return false;
+ }
+ }
+
+ return ipv6Bytes[10] == (byte) 0xff && ipv6Bytes[11] == (byte) 0xff;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/IntegerToEnglish.java b/src/main/java/com/thealgorithms/conversions/IntegerToEnglish.java
new file mode 100644
index 000000000000..e85c608af5d0
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/IntegerToEnglish.java
@@ -0,0 +1,108 @@
+package com.thealgorithms.conversions;
+
+import java.util.Map;
+
+/**
+ * A utility class to convert integers to their English word representation.
+ *
+ *
The class supports conversion of numbers from 0 to 2,147,483,647
+ * (the maximum value of a 32-bit signed integer). It divides the number
+ * into groups of three digits (thousands, millions, billions, etc.) and
+ * translates each group into words.
Conversion is based on repeatedly subtracting the largest possible Roman numeral value
+ * from the input number until it reaches zero. For example, 1994 is converted as:
+ *
+ * 1994 -> MCMXCIV (1000 + 900 + 90 + 4)
+ *
*/
-public class IntegerToRoman {
+public final class IntegerToRoman {
+
+ // Array of Roman numeral values in descending order
+ private static final int[] ALL_ROMAN_NUMBERS_IN_ARABIC = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
- private static int[] allArabianRomanNumbers = new int[] {
- 1000,
- 900,
- 500,
- 400,
- 100,
- 90,
- 50,
- 40,
- 10,
- 9,
- 5,
- 4,
- 1,
- };
- private static String[] allRomanNumbers = new String[] {
- "M",
- "CM",
- "D",
- "CD",
- "C",
- "XC",
- "L",
- "XL",
- "X",
- "IX",
- "V",
- "IV",
- "I",
- };
+ // Corresponding Roman numeral symbols
+ private static final String[] ALL_ROMAN_NUMBERS = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
+
+ private IntegerToRoman() {
+ }
- // Value must be > 0
+ /**
+ * Converts an integer to its Roman numeral representation.
+ * Steps:
+ *
+ *
Iterate over the Roman numeral values in descending order
+ *
Calculate how many times a numeral fits
+ *
Append the corresponding symbol
+ *
Subtract the value from the number
+ *
Repeat until the number is zero
+ *
Return the Roman numeral representation
+ *
+ *
+ * @param num the integer value to convert (must be greater than 0)
+ * @return the Roman numeral representation of the input integer
+ * or an empty string if the input is non-positive
+ */
public static String integerToRoman(int num) {
if (num <= 0) {
return "";
}
StringBuilder builder = new StringBuilder();
-
- for (int a = 0; a < allArabianRomanNumbers.length; a++) {
- int times = num / allArabianRomanNumbers[a];
- for (int b = 0; b < times; b++) {
- builder.append(allRomanNumbers[a]);
- }
-
- num -= times * allArabianRomanNumbers[a];
+ for (int i = 0; i < ALL_ROMAN_NUMBERS_IN_ARABIC.length; i++) {
+ int times = num / ALL_ROMAN_NUMBERS_IN_ARABIC[i];
+ builder.append(ALL_ROMAN_NUMBERS[i].repeat(Math.max(0, times)));
+ num -= times * ALL_ROMAN_NUMBERS_IN_ARABIC[i];
}
return builder.toString();
}
-
- public static void main(String[] args) {
- System.out.println(IntegerToRoman.integerToRoman(2131));
- }
}
diff --git a/src/main/java/com/thealgorithms/conversions/MorseCodeConverter.java b/src/main/java/com/thealgorithms/conversions/MorseCodeConverter.java
new file mode 100644
index 000000000000..a3973da0c586
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/MorseCodeConverter.java
@@ -0,0 +1,98 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Converts text to Morse code and vice-versa.
+ * Text to Morse code: Each letter is separated by a space and each word is separated by a pipe (|).
+ * Example: "HELLO WORLD" -> ".... . .-.. .-.. --- | .-- --- .-. .-.. -.."
+ *
+ * Morse code to text: Each letter is separated by a space and each word is separated by a pipe (|).
+ * Example: ".... . .-.. .-.. --- | .-- --- .-. .-.. -.." -> "HELLO WORLD"
+ *
+ * Applications: Used in radio communications and algorithmic challenges.
+ *
+ * @author Hardvan
+ */
+public final class MorseCodeConverter {
+ private MorseCodeConverter() {
+ }
+
+ private static final Map MORSE_MAP = new HashMap<>();
+ private static final Map REVERSE_MAP = new HashMap<>();
+
+ static {
+ MORSE_MAP.put('A', ".-");
+ MORSE_MAP.put('B', "-...");
+ MORSE_MAP.put('C', "-.-.");
+ MORSE_MAP.put('D', "-..");
+ MORSE_MAP.put('E', ".");
+ MORSE_MAP.put('F', "..-.");
+ MORSE_MAP.put('G', "--.");
+ MORSE_MAP.put('H', "....");
+ MORSE_MAP.put('I', "..");
+ MORSE_MAP.put('J', ".---");
+ MORSE_MAP.put('K', "-.-");
+ MORSE_MAP.put('L', ".-..");
+ MORSE_MAP.put('M', "--");
+ MORSE_MAP.put('N', "-.");
+ MORSE_MAP.put('O', "---");
+ MORSE_MAP.put('P', ".--.");
+ MORSE_MAP.put('Q', "--.-");
+ MORSE_MAP.put('R', ".-.");
+ MORSE_MAP.put('S', "...");
+ MORSE_MAP.put('T', "-");
+ MORSE_MAP.put('U', "..-");
+ MORSE_MAP.put('V', "...-");
+ MORSE_MAP.put('W', ".--");
+ MORSE_MAP.put('X', "-..-");
+ MORSE_MAP.put('Y', "-.--");
+ MORSE_MAP.put('Z', "--..");
+
+ // Build reverse map for decoding
+ MORSE_MAP.forEach((k, v) -> REVERSE_MAP.put(v, k));
+ }
+
+ /**
+ * Converts text to Morse code.
+ * Each letter is separated by a space and each word is separated by a pipe (|).
+ *
+ * @param text The text to convert to Morse code.
+ * @return The Morse code representation of the text.
+ */
+ public static String textToMorse(String text) {
+ StringBuilder morse = new StringBuilder();
+ String[] words = text.toUpperCase().split(" ");
+ for (int i = 0; i < words.length; i++) {
+ for (char c : words[i].toCharArray()) {
+ morse.append(MORSE_MAP.getOrDefault(c, "")).append(" ");
+ }
+ if (i < words.length - 1) {
+ morse.append("| ");
+ }
+ }
+ return morse.toString().trim();
+ }
+
+ /**
+ * Converts Morse code to text.
+ * Each letter is separated by a space and each word is separated by a pipe (|).
+ *
+ * @param morse The Morse code to convert to text.
+ * @return The text representation of the Morse code.
+ */
+ public static String morseToText(String morse) {
+ StringBuilder text = new StringBuilder();
+ String[] words = morse.split(" \\| ");
+ for (int i = 0; i < words.length; i++) {
+ for (String code : words[i].split(" ")) {
+ text.append(REVERSE_MAP.getOrDefault(code, '?'));
+ }
+ if (i < words.length - 1) {
+ text.append(" ");
+ }
+ }
+ return text.toString();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/NumberToWords.java b/src/main/java/com/thealgorithms/conversions/NumberToWords.java
new file mode 100644
index 000000000000..e39c5b2dea86
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/NumberToWords.java
@@ -0,0 +1,100 @@
+package com.thealgorithms.conversions;
+
+import java.math.BigDecimal;
+
+/**
+ A Java-based utility for converting numeric values into their English word
+ representations. Whether you need to convert a small number, a large number
+ with millions and billions, or even a number with decimal places, this utility
+ has you covered.
+ *
+ */
+public final class NumberToWords {
+
+ private NumberToWords() {
+ }
+
+ private static final String[] UNITS = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
+
+ private static final String[] TENS = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
+
+ private static final String[] POWERS = {"", "Thousand", "Million", "Billion", "Trillion"};
+
+ private static final String ZERO = "Zero";
+ private static final String POINT = " Point";
+ private static final String NEGATIVE = "Negative ";
+
+ public static String convert(BigDecimal number) {
+ if (number == null) {
+ return "Invalid Input";
+ }
+
+ // Check for negative sign
+ boolean isNegative = number.signum() < 0;
+
+ // Split the number into whole and fractional parts
+ BigDecimal[] parts = number.abs().divideAndRemainder(BigDecimal.ONE);
+ BigDecimal wholePart = parts[0]; // Keep whole part as BigDecimal
+ String fractionalPartStr = parts[1].compareTo(BigDecimal.ZERO) > 0 ? parts[1].toPlainString().substring(2) : ""; // Get fractional part only if it exists
+
+ // Convert whole part to words
+ StringBuilder result = new StringBuilder();
+ if (isNegative) {
+ result.append(NEGATIVE);
+ }
+ result.append(convertWholeNumberToWords(wholePart));
+
+ // Convert fractional part to words
+ if (!fractionalPartStr.isEmpty()) {
+ result.append(POINT);
+ for (char digit : fractionalPartStr.toCharArray()) {
+ int digitValue = Character.getNumericValue(digit);
+ result.append(" ").append(digitValue == 0 ? ZERO : UNITS[digitValue]);
+ }
+ }
+
+ return result.toString().trim();
+ }
+
+ private static String convertWholeNumberToWords(BigDecimal number) {
+ if (number.compareTo(BigDecimal.ZERO) == 0) {
+ return ZERO;
+ }
+
+ StringBuilder words = new StringBuilder();
+ int power = 0;
+
+ while (number.compareTo(BigDecimal.ZERO) > 0) {
+ // Get the last three digits
+ BigDecimal[] divisionResult = number.divideAndRemainder(BigDecimal.valueOf(1000));
+ int chunk = divisionResult[1].intValue();
+
+ if (chunk > 0) {
+ String chunkWords = convertChunk(chunk);
+ if (power > 0) {
+ words.insert(0, POWERS[power] + " ");
+ }
+ words.insert(0, chunkWords + " ");
+ }
+
+ number = divisionResult[0]; // Continue with the remaining part
+ power++;
+ }
+
+ return words.toString().trim();
+ }
+
+ private static String convertChunk(int number) {
+ String chunkWords;
+
+ if (number < 20) {
+ chunkWords = UNITS[number];
+ } else if (number < 100) {
+ chunkWords = TENS[number / 10] + (number % 10 > 0 ? " " + UNITS[number % 10] : "");
+ } else {
+ chunkWords = UNITS[number / 100] + " Hundred" + (number % 100 > 0 ? " " + convertChunk(number % 100) : "");
+ }
+
+ return chunkWords;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/OctalToBinary.java b/src/main/java/com/thealgorithms/conversions/OctalToBinary.java
index 711381d82a8e..a66db97633b4 100644
--- a/src/main/java/com/thealgorithms/conversions/OctalToBinary.java
+++ b/src/main/java/com/thealgorithms/conversions/OctalToBinary.java
@@ -1,13 +1,40 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
/**
- * Converts any Octal Number to a Binary Number
+ * A utility class to convert an octal (base-8) number into its binary (base-2) representation.
+ *
+ *
This class provides methods to:
+ *
+ *
Convert an octal number to its binary equivalent
+ *
Convert individual octal digits to binary
+ *
+ *
+ *
Octal to Binary Conversion:
+ *
An octal number is converted to binary by converting each octal digit to its 3-bit binary equivalent.
+ * The result is a long representing the full binary equivalent of the octal number.
+ *
+ *
Example Usage
+ *
+ * long binary = OctalToBinary.convertOctalToBinary(52); // Output: 101010 (52 in octal is 101010 in binary)
+ *
*
* @author Bama Charan Chhandogi
+ * @see Octal Number System
+ * @see Binary Number System
*/
+public final class OctalToBinary {
+ private OctalToBinary() {
+ }
-public class OctalToBinary {
+ /**
+ * Converts an octal number to its binary representation.
+ *
+ *
Each octal digit is individually converted to its 3-bit binary equivalent, and the binary
+ * digits are concatenated to form the final binary number.
+ *
+ * @param octalNumber the octal number to convert (non-negative integer)
+ * @return the binary equivalent as a long
+ */
public static long convertOctalToBinary(int octalNumber) {
long binaryNumber = 0;
int digitPosition = 1;
@@ -19,12 +46,25 @@ public static long convertOctalToBinary(int octalNumber) {
binaryNumber += binaryDigit * digitPosition;
octalNumber /= 10;
- digitPosition *= 1000; // Move to the next group of 3 binary digits
+ digitPosition *= 1000;
}
return binaryNumber;
}
+ /**
+ * Converts a single octal digit (0-7) to its binary equivalent.
+ *
+ *
For example:
+ *
+ *
Octal digit 7 is converted to binary 111
+ *
Octal digit 3 is converted to binary 011
+ *
+ *
+ *
+ * @param octalDigit a single octal digit (0-7)
+ * @return the binary equivalent as a long
+ */
public static long convertOctalDigitToBinary(int octalDigit) {
long binaryDigit = 0;
int binaryMultiplier = 1;
diff --git a/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java b/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
index d4916a3dbcca..d91ce6eb3634 100644
--- a/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java
@@ -1,45 +1,42 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
- * Converts any Octal Number to a Decimal Number
+ * Class for converting an octal number to a decimal number. Octal numbers are based on 8, using digits from 0 to 7.
*
- * @author Zachary Jones
*/
-public class OctalToDecimal {
+public final class OctalToDecimal {
+ private static final int OCTAL_BASE = 8;
- /**
- * Main method
- *
- * @param args Command line arguments
- */
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- System.out.print("Octal Input: ");
- String inputOctal = sc.nextLine();
- int result = convertOctalToDecimal(inputOctal);
- if (result != -1) {
- System.out.println("Result convertOctalToDecimal : " + result);
- }
- sc.close();
+ private OctalToDecimal() {
}
/**
- * This method converts an octal number to a decimal number.
+ * Converts a given octal number (as a string) to its decimal representation.
+ * If the input is not a valid octal number (i.e., contains characters other than 0-7),
+ * the method throws an IllegalArgumentException.
*
- * @param inputOctal The octal number
- * @return The decimal number
+ * @param inputOctal The octal number as a string
+ * @return The decimal equivalent of the octal number
+ * @throws IllegalArgumentException if the input is not a valid octal number
*/
public static int convertOctalToDecimal(String inputOctal) {
- try {
- // Actual conversion of Octal to Decimal:
- return Integer.parseInt(inputOctal, 8);
- } catch (NumberFormatException ne) {
- // Printing a warning message if the input is not a valid octal
- // number:
- System.out.println("Invalid Input, Expecting octal number 0-7");
- return -1;
+ if (inputOctal == null || inputOctal.isEmpty()) {
+ throw new IllegalArgumentException("Input cannot be null or empty");
}
+
+ int decimalValue = 0;
+
+ for (int i = 0; i < inputOctal.length(); i++) {
+ char currentChar = inputOctal.charAt(i);
+
+ if (currentChar < '0' || currentChar > '7') {
+ throw new IllegalArgumentException("Incorrect input: Expecting an octal number (digits 0-7)");
+ }
+
+ int currentDigit = currentChar - '0';
+ decimalValue = decimalValue * OCTAL_BASE + currentDigit;
+ }
+
+ return decimalValue;
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/OctalToHexadecimal.java b/src/main/java/com/thealgorithms/conversions/OctalToHexadecimal.java
index 5edd94c38430..bac56dc2e221 100644
--- a/src/main/java/com/thealgorithms/conversions/OctalToHexadecimal.java
+++ b/src/main/java/com/thealgorithms/conversions/OctalToHexadecimal.java
@@ -1,63 +1,61 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
- * Converts any Octal Number to HexaDecimal
+ * Class for converting an Octal number to its Hexadecimal equivalent.
*
* @author Tanmay Joshi
*/
-public class OctalToHexadecimal {
+public final class OctalToHexadecimal {
+ private static final int OCTAL_BASE = 8;
+ private static final int HEX_BASE = 16;
+ private static final String HEX_DIGITS = "0123456789ABCDEF";
+
+ private OctalToHexadecimal() {
+ }
/**
- * This method converts a Octal number to a decimal number
+ * Converts an Octal number (as a string) to its Decimal equivalent.
*
- * @param s The Octal Number
- * @return The Decimal number
+ * @param octalNumber The Octal number as a string
+ * @return The Decimal equivalent of the Octal number
+ * @throws IllegalArgumentException if the input contains invalid octal digits
*/
- public static int octToDec(String s) {
- int i = 0;
- for (int j = 0; j < s.length(); j++) {
- char num = s.charAt(j);
- num -= '0';
- i *= 8;
- i += num;
+ public static int octalToDecimal(String octalNumber) {
+ if (octalNumber == null || octalNumber.isEmpty()) {
+ throw new IllegalArgumentException("Input cannot be null or empty");
+ }
+
+ int decimalValue = 0;
+ for (int i = 0; i < octalNumber.length(); i++) {
+ char currentChar = octalNumber.charAt(i);
+ if (currentChar < '0' || currentChar > '7') {
+ throw new IllegalArgumentException("Incorrect octal digit: " + currentChar);
+ }
+ int currentDigit = currentChar - '0';
+ decimalValue = decimalValue * OCTAL_BASE + currentDigit;
}
- return i;
+
+ return decimalValue;
}
/**
- * This method converts a Decimal number to a Hexadecimal number
+ * Converts a Decimal number to its Hexadecimal equivalent.
*
- * @param d The Decimal Number
- * @return The Hexadecimal number
+ * @param decimalNumber The Decimal number
+ * @return The Hexadecimal equivalent of the Decimal number
*/
- public static String decimalToHex(int d) {
- String digits = "0123456789ABCDEF";
- if (d <= 0) {
+ public static String decimalToHexadecimal(int decimalNumber) {
+ if (decimalNumber == 0) {
return "0";
}
- String hex = "";
- while (d > 0) {
- int digit = d % 16;
- hex = digits.charAt(digit) + hex;
- d = d / 16;
- }
- return hex;
- }
- public static void main(String[] args) {
- Scanner input = new Scanner(System.in);
- System.out.print("Enter the Octal number: ");
- // Take octal number as input from user in a string
- String oct = input.next();
-
- // Pass the octal number to function and get converted decimal form
- int decimal = octToDec(oct);
+ StringBuilder hexValue = new StringBuilder();
+ while (decimalNumber > 0) {
+ int digit = decimalNumber % HEX_BASE;
+ hexValue.insert(0, HEX_DIGITS.charAt(digit));
+ decimalNumber /= HEX_BASE;
+ }
- // Pass the decimal number to function and get converted Hex form of the number
- String hex = decimalToHex(decimal);
- System.out.println("The Hexadecimal equivalant is: " + hex);
- input.close();
+ return hexValue.toString();
}
}
diff --git a/src/main/java/com/thealgorithms/conversions/PhoneticAlphabetConverter.java b/src/main/java/com/thealgorithms/conversions/PhoneticAlphabetConverter.java
new file mode 100644
index 000000000000..730ce2214e2d
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/PhoneticAlphabetConverter.java
@@ -0,0 +1,84 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Converts text to the NATO phonetic alphabet.
+ * Examples:
+ * "ABC" -> "Alpha Bravo Charlie"
+ * "Hello" -> "Hotel Echo Lima Lima Oscar"
+ * "123" -> "One Two Three"
+ * "A1B2C3" -> "Alpha One Bravo Two Charlie Three"
+ *
+ * @author Hardvan
+ */
+public final class PhoneticAlphabetConverter {
+ private PhoneticAlphabetConverter() {
+ }
+
+ private static final Map PHONETIC_MAP = new HashMap<>();
+
+ static {
+ PHONETIC_MAP.put('A', "Alpha");
+ PHONETIC_MAP.put('B', "Bravo");
+ PHONETIC_MAP.put('C', "Charlie");
+ PHONETIC_MAP.put('D', "Delta");
+ PHONETIC_MAP.put('E', "Echo");
+ PHONETIC_MAP.put('F', "Foxtrot");
+ PHONETIC_MAP.put('G', "Golf");
+ PHONETIC_MAP.put('H', "Hotel");
+ PHONETIC_MAP.put('I', "India");
+ PHONETIC_MAP.put('J', "Juliett");
+ PHONETIC_MAP.put('K', "Kilo");
+ PHONETIC_MAP.put('L', "Lima");
+ PHONETIC_MAP.put('M', "Mike");
+ PHONETIC_MAP.put('N', "November");
+ PHONETIC_MAP.put('O', "Oscar");
+ PHONETIC_MAP.put('P', "Papa");
+ PHONETIC_MAP.put('Q', "Quebec");
+ PHONETIC_MAP.put('R', "Romeo");
+ PHONETIC_MAP.put('S', "Sierra");
+ PHONETIC_MAP.put('T', "Tango");
+ PHONETIC_MAP.put('U', "Uniform");
+ PHONETIC_MAP.put('V', "Victor");
+ PHONETIC_MAP.put('W', "Whiskey");
+ PHONETIC_MAP.put('X', "X-ray");
+ PHONETIC_MAP.put('Y', "Yankee");
+ PHONETIC_MAP.put('Z', "Zulu");
+ PHONETIC_MAP.put('0', "Zero");
+ PHONETIC_MAP.put('1', "One");
+ PHONETIC_MAP.put('2', "Two");
+ PHONETIC_MAP.put('3', "Three");
+ PHONETIC_MAP.put('4', "Four");
+ PHONETIC_MAP.put('5', "Five");
+ PHONETIC_MAP.put('6', "Six");
+ PHONETIC_MAP.put('7', "Seven");
+ PHONETIC_MAP.put('8', "Eight");
+ PHONETIC_MAP.put('9', "Nine");
+ }
+
+ /**
+ * Converts text to the NATO phonetic alphabet.
+ * Steps:
+ * 1. Convert the text to uppercase.
+ * 2. Iterate over each character in the text.
+ * 3. Get the phonetic equivalent of the character from the map.
+ * 4. Append the phonetic equivalent to the result.
+ * 5. Append a space to separate the phonetic equivalents.
+ * 6. Return the result.
+ *
+ * @param text the text to convert
+ * @return the NATO phonetic alphabet
+ */
+ public static String textToPhonetic(String text) {
+ StringBuilder phonetic = new StringBuilder();
+ for (char c : text.toUpperCase().toCharArray()) {
+ if (Character.isWhitespace(c)) {
+ continue;
+ }
+ phonetic.append(PHONETIC_MAP.getOrDefault(c, String.valueOf(c))).append(" ");
+ }
+ return phonetic.toString().trim();
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/RgbHsvConversion.java b/src/main/java/com/thealgorithms/conversions/RgbHsvConversion.java
index ca64c3ffd7a6..84cbff09db6b 100644
--- a/src/main/java/com/thealgorithms/conversions/RgbHsvConversion.java
+++ b/src/main/java/com/thealgorithms/conversions/RgbHsvConversion.java
@@ -10,10 +10,12 @@
* models how colors appear under light. In it, colors are represented using
* three components: hue, saturation and (brightness-)value. This class provides
* methods for converting colors from one representation to the other.
- * (description adapted from https://en.wikipedia.org/wiki/RGB_color_model and
- * https://en.wikipedia.org/wiki/HSL_and_HSV).
+ * (description adapted from [1] and
+ * [2]).
*/
-public class RgbHsvConversion {
+public final class RgbHsvConversion {
+ private RgbHsvConversion() {
+ }
public static void main(String[] args) {
// Expected RGB-values taken from https://www.rapidtables.com/convert/color/hsv-to-rgb.html
diff --git a/src/main/java/com/thealgorithms/conversions/RomanToInteger.java b/src/main/java/com/thealgorithms/conversions/RomanToInteger.java
index fddb56232c58..a634c720326f 100644
--- a/src/main/java/com/thealgorithms/conversions/RomanToInteger.java
+++ b/src/main/java/com/thealgorithms/conversions/RomanToInteger.java
@@ -1,14 +1,31 @@
package com.thealgorithms.conversions;
-import java.util.*;
+import java.util.HashMap;
+import java.util.Map;
-public class RomanToInteger {
-
- private static Map map = new HashMap() {
- /**
- * */
- private static final long serialVersionUID = 87605733047260530L;
+/**
+ * A utility class to convert Roman numerals into integers.
+ *
+ *
Roman numerals are based on seven symbols given below:
+ *
+ *
I = 1
+ *
V = 5
+ *
X = 10
+ *
L = 50
+ *
C = 100
+ *
D = 500
+ *
M = 1000
+ *
+ *
+ *
If a smaller numeral appears before a larger numeral, it is subtracted.
+ * Otherwise, it is added. For example:
+ *
+ */
+public final class RomanToInteger {
+ private static final Map ROMAN_TO_INT = new HashMap<>() {
{
put('I', 1);
put('V', 5);
@@ -20,47 +37,55 @@ public class RomanToInteger {
}
};
- // Roman Number = Roman Numerals
+ private RomanToInteger() {
+ }
/**
- * This function convert Roman number into Integer
+ * Converts a single Roman numeral character to its integer value.
*
- * @param A Roman number string
- * @return integer
+ * @param symbol the Roman numeral character
+ * @return the corresponding integer value
+ * @throws IllegalArgumentException if the symbol is not a valid Roman numeral
*/
- public static int romanToInt(String A) {
- A = A.toUpperCase();
- char prev = ' ';
-
- int sum = 0;
-
- int newPrev = 0;
- for (int i = A.length() - 1; i >= 0; i--) {
- char c = A.charAt(i);
-
- if (prev != ' ') {
- // checking current Number greater then previous or not
- newPrev = map.get(prev) > newPrev ? map.get(prev) : newPrev;
- }
+ private static int romanSymbolToInt(final char symbol) {
+ return ROMAN_TO_INT.computeIfAbsent(symbol, c -> { throw new IllegalArgumentException("Unknown Roman symbol: " + c); });
+ }
- int currentNum = map.get(c);
+ /**
+ * Converts a Roman numeral string to its integer equivalent.
+ * Steps:
+ *
+ *
Iterate over the string from right to left.
+ *
For each character, convert it to an integer value.
+ *
If the current value is greater than or equal to the max previous value, add it.
+ *
Otherwise, subtract it from the sum.
+ *
Update the max previous value.
+ *
Return the sum.
+ *
+ *
+ * @param roman the Roman numeral string
+ * @return the integer value of the Roman numeral
+ * @throws IllegalArgumentException if the input contains invalid Roman characters
+ * @throws NullPointerException if the input is {@code null}
+ */
+ public static int romanToInt(String roman) {
+ if (roman == null) {
+ throw new NullPointerException("Input cannot be null");
+ }
- // if current number greater then prev max previous then add
- if (currentNum >= newPrev) {
- sum += currentNum;
+ roman = roman.toUpperCase();
+ int sum = 0;
+ int maxPrevValue = 0;
+ for (int i = roman.length() - 1; i >= 0; i--) {
+ int currentValue = romanSymbolToInt(roman.charAt(i));
+ if (currentValue >= maxPrevValue) {
+ sum += currentValue;
+ maxPrevValue = currentValue;
} else {
- // subtract upcoming number until upcoming number not greater then prev max
- sum -= currentNum;
+ sum -= currentValue;
}
-
- prev = c;
}
return sum;
}
-
- public static void main(String[] args) {
- int sum = romanToInt("MDCCCIV");
- System.out.println(sum);
- }
}
diff --git a/src/main/java/com/thealgorithms/conversions/TurkishToLatinConversion.java b/src/main/java/com/thealgorithms/conversions/TurkishToLatinConversion.java
index d991f5f31faf..30030de6c1bd 100644
--- a/src/main/java/com/thealgorithms/conversions/TurkishToLatinConversion.java
+++ b/src/main/java/com/thealgorithms/conversions/TurkishToLatinConversion.java
@@ -1,29 +1,20 @@
package com.thealgorithms.conversions;
-import java.util.Scanner;
-
/**
* Converts turkish character to latin character
*
* @author Özgün Gökşenli
*/
-public class TurkishToLatinConversion {
-
- /**
- * Main method
- *
- * @param args Command line arguments
- */
- public static void main(String[] args) {
- Scanner sc = new Scanner(System.in);
- System.out.println("Input the string: ");
- String b = sc.next();
- System.out.println("Converted: " + convertTurkishToLatin(b));
- sc.close();
+public final class TurkishToLatinConversion {
+ private TurkishToLatinConversion() {
}
/**
* This method converts a turkish character to latin character.
+ * Steps:
+ * 1. Define turkish characters and their corresponding latin characters
+ * 2. Replace all turkish characters with their corresponding latin characters
+ * 3. Return the converted string
*
* @param param String paramter
* @return String
@@ -58,7 +49,7 @@ public static String convertTurkishToLatin(String param) {
'G',
};
for (int i = 0; i < turkishChars.length; i++) {
- param = param.replaceAll(new String(new char[] {turkishChars[i]}), new String(new char[] {latinChars[i]}));
+ param = param.replaceAll(String.valueOf(turkishChars[i]), String.valueOf(latinChars[i]));
}
return param;
}
diff --git a/src/main/java/com/thealgorithms/conversions/UnitConversions.java b/src/main/java/com/thealgorithms/conversions/UnitConversions.java
new file mode 100644
index 000000000000..15f74a21a17e
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/UnitConversions.java
@@ -0,0 +1,51 @@
+package com.thealgorithms.conversions;
+
+import static java.util.Map.entry;
+
+import java.util.Map;
+import org.apache.commons.lang3.tuple.Pair;
+
+/**
+ * A utility class to perform unit conversions between different measurement systems.
+ *
+ *
Currently, the class supports temperature conversions between several scales:
+ * Celsius, Fahrenheit, Kelvin, Réaumur, Delisle, and Rankine.
+ *
+ *
Example Usage
+ *
+ * double result = UnitConversions.TEMPERATURE.convert("Celsius", "Fahrenheit", 100.0);
+ * // Output: 212.0 (Celsius to Fahrenheit conversion of 100°C)
+ *
+ *
+ *
This class makes use of an {@link UnitsConverter} that handles the conversion logic
+ * based on predefined affine transformations. These transformations include scaling factors
+ * and offsets for temperature conversions.
+ *
+ *
Temperature Scales Supported
+ *
+ *
Celsius
+ *
Fahrenheit
+ *
Kelvin
+ *
Réaumur
+ *
Delisle
+ *
Rankine
+ *
+ */
+public final class UnitConversions {
+ private UnitConversions() {
+ }
+
+ /**
+ * A preconfigured instance of {@link UnitsConverter} for temperature conversions.
+ * The converter handles conversions between the following temperature units:
+ *
+ *
Kelvin to Celsius
+ *
Celsius to Fahrenheit
+ *
Réaumur to Celsius
+ *
Delisle to Celsius
+ *
Rankine to Kelvin
+ *
+ */
+ public static final UnitsConverter TEMPERATURE = new UnitsConverter(Map.ofEntries(entry(Pair.of("Kelvin", "Celsius"), new AffineConverter(1.0, -273.15)), entry(Pair.of("Celsius", "Fahrenheit"), new AffineConverter(9.0 / 5.0, 32.0)),
+ entry(Pair.of("Réaumur", "Celsius"), new AffineConverter(5.0 / 4.0, 0.0)), entry(Pair.of("Delisle", "Celsius"), new AffineConverter(-2.0 / 3.0, 100.0)), entry(Pair.of("Rankine", "Kelvin"), new AffineConverter(5.0 / 9.0, 0.0))));
+}
diff --git a/src/main/java/com/thealgorithms/conversions/UnitsConverter.java b/src/main/java/com/thealgorithms/conversions/UnitsConverter.java
new file mode 100644
index 000000000000..00690b2c0f9b
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/UnitsConverter.java
@@ -0,0 +1,147 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import org.apache.commons.lang3.tuple.Pair;
+
+/**
+ * A class that handles unit conversions using affine transformations.
+ *
+ *
The {@code UnitsConverter} allows converting values between different units using
+ * pre-defined affine conversion formulas. Each conversion is represented by an
+ * {@link AffineConverter} that defines the scaling and offset for the conversion.
+ *
+ *
For each unit, both direct conversions (e.g., Celsius to Fahrenheit) and inverse
+ * conversions (e.g., Fahrenheit to Celsius) are generated automatically. It also computes
+ * transitive conversions (e.g., Celsius to Kelvin via Fahrenheit if both conversions exist).
+ *
+ *
Key features include:
+ *
+ *
Automatic handling of inverse conversions (e.g., Fahrenheit to Celsius).
+ *
Compositional conversions, meaning if conversions between A -> B and B -> C exist,
+ * it can automatically generate A -> C conversion.
+ *
Supports multiple unit systems as long as conversions are provided in pairs.
+ *
+ *
+ *
Example Usage
+ *
+ * Map<Pair<String, String>, AffineConverter> basicConversions = Map.ofEntries(
+ * entry(Pair.of("Celsius", "Fahrenheit"), new AffineConverter(9.0 / 5.0, 32.0)),
+ * entry(Pair.of("Kelvin", "Celsius"), new AffineConverter(1.0, -273.15))
+ * );
+ *
+ * UnitsConverter converter = new UnitsConverter(basicConversions);
+ * double result = converter.convert("Celsius", "Fahrenheit", 100.0);
+ * // Output: 212.0 (Celsius to Fahrenheit conversion of 100°C)
+ *
+ *
+ *
Exception Handling
+ *
+ *
If the input unit and output unit are the same, an {@link IllegalArgumentException} is thrown.
+ *
If a conversion between the requested units does not exist, a {@link NoSuchElementException} is thrown.
+ *
+ */
+public final class UnitsConverter {
+ private final Map, AffineConverter> conversions;
+ private final Set units;
+
+ private static void putIfNeeded(Map, AffineConverter> conversions, final String inputUnit, final String outputUnit, final AffineConverter converter) {
+ if (!inputUnit.equals(outputUnit)) {
+ final var key = Pair.of(inputUnit, outputUnit);
+ conversions.putIfAbsent(key, converter);
+ }
+ }
+
+ private static Map, AffineConverter> addInversions(final Map, AffineConverter> knownConversions) {
+ Map, AffineConverter> res = new HashMap, AffineConverter>();
+ for (final var curConversion : knownConversions.entrySet()) {
+ final var inputUnit = curConversion.getKey().getKey();
+ final var outputUnit = curConversion.getKey().getValue();
+ putIfNeeded(res, inputUnit, outputUnit, curConversion.getValue());
+ putIfNeeded(res, outputUnit, inputUnit, curConversion.getValue().invert());
+ }
+ return res;
+ }
+
+ private static Map, AffineConverter> addCompositions(final Map, AffineConverter> knownConversions) {
+ Map, AffineConverter> res = new HashMap, AffineConverter>();
+ for (final var first : knownConversions.entrySet()) {
+ final var firstKey = first.getKey();
+ putIfNeeded(res, firstKey.getKey(), firstKey.getValue(), first.getValue());
+ for (final var second : knownConversions.entrySet()) {
+ final var secondKey = second.getKey();
+ if (firstKey.getValue().equals(secondKey.getKey())) {
+ final var newConversion = second.getValue().compose(first.getValue());
+ putIfNeeded(res, firstKey.getKey(), secondKey.getValue(), newConversion);
+ }
+ }
+ }
+ return res;
+ }
+
+ private static Map, AffineConverter> addAll(final Map, AffineConverter> knownConversions) {
+ final var res = addInversions(knownConversions);
+ return addCompositions(res);
+ }
+
+ private static Map, AffineConverter> computeAllConversions(final Map, AffineConverter> basicConversions) {
+ var tmp = basicConversions;
+ var res = addAll(tmp);
+ while (res.size() != tmp.size()) {
+ tmp = res;
+ res = addAll(tmp);
+ }
+ return res;
+ }
+
+ private static Set extractUnits(final Map, AffineConverter> conversions) {
+ Set res = new HashSet<>();
+ for (final var conversion : conversions.entrySet()) {
+ res.add(conversion.getKey().getKey());
+ }
+ return res;
+ }
+
+ /**
+ * Constructor for {@code UnitsConverter}.
+ *
+ *
Accepts a map of basic conversions and automatically generates inverse and
+ * transitive conversions.
+ *
+ * @param basicConversions the initial set of unit conversions to add.
+ */
+ public UnitsConverter(final Map, AffineConverter> basicConversions) {
+ conversions = computeAllConversions(basicConversions);
+ units = extractUnits(conversions);
+ }
+
+ /**
+ * Converts a value from one unit to another.
+ *
+ * @param inputUnit the unit of the input value.
+ * @param outputUnit the unit to convert the value into.
+ * @param value the value to convert.
+ * @return the converted value in the target unit.
+ * @throws IllegalArgumentException if inputUnit equals outputUnit.
+ * @throws NoSuchElementException if no conversion exists between the units.
+ */
+ public double convert(final String inputUnit, final String outputUnit, final double value) {
+ if (inputUnit.equals(outputUnit)) {
+ throw new IllegalArgumentException("inputUnit must be different from outputUnit.");
+ }
+ final var conversionKey = Pair.of(inputUnit, outputUnit);
+ return conversions.computeIfAbsent(conversionKey, k -> { throw new NoSuchElementException("No converter for: " + k); }).convert(value);
+ }
+
+ /**
+ * Retrieves the set of all units supported by this converter.
+ *
+ * @return a set of available units.
+ */
+ public Set availableUnits() {
+ return units;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/WordsToNumber.java b/src/main/java/com/thealgorithms/conversions/WordsToNumber.java
new file mode 100644
index 000000000000..e2b81a0f4b47
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/WordsToNumber.java
@@ -0,0 +1,343 @@
+package com.thealgorithms.conversions;
+
+import java.io.Serial;
+import java.math.BigDecimal;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ A Java-based utility for converting English word representations of numbers
+ into their numeric form. This utility supports whole numbers, decimals,
+ large values up to trillions, and even scientific notation where applicable.
+ It ensures accurate parsing while handling edge cases like negative numbers,
+ improper word placements, and ambiguous inputs.
+ *
+ */
+
+public final class WordsToNumber {
+
+ private WordsToNumber() {
+ }
+
+ private enum NumberWord {
+ ZERO("zero", 0),
+ ONE("one", 1),
+ TWO("two", 2),
+ THREE("three", 3),
+ FOUR("four", 4),
+ FIVE("five", 5),
+ SIX("six", 6),
+ SEVEN("seven", 7),
+ EIGHT("eight", 8),
+ NINE("nine", 9),
+ TEN("ten", 10),
+ ELEVEN("eleven", 11),
+ TWELVE("twelve", 12),
+ THIRTEEN("thirteen", 13),
+ FOURTEEN("fourteen", 14),
+ FIFTEEN("fifteen", 15),
+ SIXTEEN("sixteen", 16),
+ SEVENTEEN("seventeen", 17),
+ EIGHTEEN("eighteen", 18),
+ NINETEEN("nineteen", 19),
+ TWENTY("twenty", 20),
+ THIRTY("thirty", 30),
+ FORTY("forty", 40),
+ FIFTY("fifty", 50),
+ SIXTY("sixty", 60),
+ SEVENTY("seventy", 70),
+ EIGHTY("eighty", 80),
+ NINETY("ninety", 90);
+
+ private final String word;
+ private final int value;
+
+ NumberWord(String word, int value) {
+ this.word = word;
+ this.value = value;
+ }
+
+ public static Integer getValue(String word) {
+ for (NumberWord num : values()) {
+ if (word.equals(num.word)) {
+ return num.value;
+ }
+ }
+ return null;
+ }
+ }
+
+ private enum PowerOfTen {
+ THOUSAND("thousand", new BigDecimal("1000")),
+ MILLION("million", new BigDecimal("1000000")),
+ BILLION("billion", new BigDecimal("1000000000")),
+ TRILLION("trillion", new BigDecimal("1000000000000"));
+
+ private final String word;
+ private final BigDecimal value;
+
+ PowerOfTen(String word, BigDecimal value) {
+ this.word = word;
+ this.value = value;
+ }
+
+ public static BigDecimal getValue(String word) {
+ for (PowerOfTen power : values()) {
+ if (word.equals(power.word)) {
+ return power.value;
+ }
+ }
+ return null;
+ }
+ }
+
+ public static String convert(String numberInWords) {
+ if (numberInWords == null) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.NULL_INPUT, "");
+ }
+
+ ArrayDeque wordDeque = preprocessWords(numberInWords);
+ BigDecimal completeNumber = convertWordQueueToBigDecimal(wordDeque);
+
+ return completeNumber.toString();
+ }
+
+ public static BigDecimal convertToBigDecimal(String numberInWords) {
+ String conversionResult = convert(numberInWords);
+ return new BigDecimal(conversionResult);
+ }
+
+ private static ArrayDeque preprocessWords(String numberInWords) {
+ String[] wordSplitArray = numberInWords.trim().split("[ ,-]");
+ ArrayDeque wordDeque = new ArrayDeque<>();
+ for (String word : wordSplitArray) {
+ if (word.isEmpty()) {
+ continue;
+ }
+ wordDeque.add(word.toLowerCase());
+ }
+ if (wordDeque.isEmpty()) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.NULL_INPUT, "");
+ }
+ return wordDeque;
+ }
+
+ private static void handleConjunction(boolean prevNumWasHundred, boolean prevNumWasPowerOfTen, ArrayDeque wordDeque) {
+ if (wordDeque.isEmpty()) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.INVALID_CONJUNCTION, "");
+ }
+
+ String nextWord = wordDeque.pollFirst();
+ String afterNextWord = wordDeque.peekFirst();
+
+ wordDeque.addFirst(nextWord);
+
+ Integer number = NumberWord.getValue(nextWord);
+
+ boolean isPrevWordValid = prevNumWasHundred || prevNumWasPowerOfTen;
+ boolean isNextWordValid = number != null && (number >= 10 || afterNextWord == null || "point".equals(afterNextWord));
+
+ if (!isPrevWordValid || !isNextWordValid) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.INVALID_CONJUNCTION, "");
+ }
+ }
+
+ private static BigDecimal handleHundred(BigDecimal currentChunk, String word, boolean prevNumWasPowerOfTen) {
+ boolean currentChunkIsZero = currentChunk.compareTo(BigDecimal.ZERO) == 0;
+ if (currentChunk.compareTo(BigDecimal.TEN) >= 0 || prevNumWasPowerOfTen) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD, word);
+ }
+ if (currentChunkIsZero) {
+ currentChunk = currentChunk.add(BigDecimal.ONE);
+ }
+ return currentChunk.multiply(BigDecimal.valueOf(100));
+ }
+
+ private static void handlePowerOfTen(List chunks, BigDecimal currentChunk, BigDecimal powerOfTen, String word, boolean prevNumWasPowerOfTen) {
+ boolean currentChunkIsZero = currentChunk.compareTo(BigDecimal.ZERO) == 0;
+ if (currentChunkIsZero || prevNumWasPowerOfTen) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD, word);
+ }
+ BigDecimal nextChunk = currentChunk.multiply(powerOfTen);
+
+ if (!(chunks.isEmpty() || isAdditionSafe(chunks.getLast(), nextChunk))) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD, word);
+ }
+ chunks.add(nextChunk);
+ }
+
+ private static BigDecimal handleNumber(Collection chunks, BigDecimal currentChunk, String word, Integer number) {
+ boolean currentChunkIsZero = currentChunk.compareTo(BigDecimal.ZERO) == 0;
+ if (number == 0 && !(currentChunkIsZero && chunks.isEmpty())) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD, word);
+ }
+ BigDecimal bigDecimalNumber = BigDecimal.valueOf(number);
+
+ if (!currentChunkIsZero && !isAdditionSafe(currentChunk, bigDecimalNumber)) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD, word);
+ }
+ return currentChunk.add(bigDecimalNumber);
+ }
+
+ private static void handlePoint(Collection chunks, BigDecimal currentChunk, ArrayDeque wordDeque) {
+ boolean currentChunkIsZero = currentChunk.compareTo(BigDecimal.ZERO) == 0;
+ if (!currentChunkIsZero) {
+ chunks.add(currentChunk);
+ }
+
+ String decimalPart = convertDecimalPart(wordDeque);
+ chunks.add(new BigDecimal(decimalPart));
+ }
+
+ private static void handleNegative(boolean isNegative) {
+ if (isNegative) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.MULTIPLE_NEGATIVES, "");
+ }
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.INVALID_NEGATIVE, "");
+ }
+
+ private static BigDecimal convertWordQueueToBigDecimal(ArrayDeque wordDeque) {
+ BigDecimal currentChunk = BigDecimal.ZERO;
+ List chunks = new ArrayList<>();
+
+ boolean isNegative = "negative".equals(wordDeque.peek());
+ if (isNegative) {
+ wordDeque.poll();
+ }
+
+ boolean prevNumWasHundred = false;
+ boolean prevNumWasPowerOfTen = false;
+
+ while (!wordDeque.isEmpty()) {
+ String word = wordDeque.poll();
+
+ switch (word) {
+ case "and" -> {
+ handleConjunction(prevNumWasHundred, prevNumWasPowerOfTen, wordDeque);
+ continue;
+ }
+ case "hundred" -> {
+ currentChunk = handleHundred(currentChunk, word, prevNumWasPowerOfTen);
+ prevNumWasHundred = true;
+ continue;
+ }
+ default -> {
+
+ }
+ }
+ prevNumWasHundred = false;
+
+ BigDecimal powerOfTen = PowerOfTen.getValue(word);
+ if (powerOfTen != null) {
+ handlePowerOfTen(chunks, currentChunk, powerOfTen, word, prevNumWasPowerOfTen);
+ currentChunk = BigDecimal.ZERO;
+ prevNumWasPowerOfTen = true;
+ continue;
+ }
+ prevNumWasPowerOfTen = false;
+
+ Integer number = NumberWord.getValue(word);
+ if (number != null) {
+ currentChunk = handleNumber(chunks, currentChunk, word, number);
+ continue;
+ }
+
+ switch (word) {
+ case "point" -> {
+ handlePoint(chunks, currentChunk, wordDeque);
+ currentChunk = BigDecimal.ZERO;
+ continue;
+ }
+ case "negative" -> {
+ handleNegative(isNegative);
+ }
+ default -> {
+
+ }
+ }
+
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNKNOWN_WORD, word);
+ }
+
+ if (currentChunk.compareTo(BigDecimal.ZERO) != 0) {
+ chunks.add(currentChunk);
+ }
+
+ BigDecimal completeNumber = combineChunks(chunks);
+ return isNegative ? completeNumber.multiply(BigDecimal.valueOf(-1))
+ :
+ completeNumber;
+ }
+
+ private static boolean isAdditionSafe(BigDecimal currentChunk, BigDecimal number) {
+ int chunkDigitCount = currentChunk.toString().length();
+ int numberDigitCount = number.toString().length();
+ return chunkDigitCount > numberDigitCount;
+ }
+
+ private static String convertDecimalPart(ArrayDeque wordDeque) {
+ StringBuilder decimalPart = new StringBuilder(".");
+
+ while (!wordDeque.isEmpty()) {
+ String word = wordDeque.poll();
+ Integer number = NumberWord.getValue(word);
+ if (number == null) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.UNEXPECTED_WORD_AFTER_POINT, word);
+ }
+ decimalPart.append(number);
+ }
+
+ boolean missingNumbers = decimalPart.length() == 1;
+ if (missingNumbers) {
+ throw new WordsToNumberException(WordsToNumberException.ErrorType.MISSING_DECIMAL_NUMBERS, "");
+ }
+ return decimalPart.toString();
+ }
+
+ private static BigDecimal combineChunks(List chunks) {
+ BigDecimal completeNumber = BigDecimal.ZERO;
+ for (BigDecimal chunk : chunks) {
+ completeNumber = completeNumber.add(chunk);
+ }
+ return completeNumber;
+ }
+ }
+
+ class WordsToNumberException extends RuntimeException {
+
+ @Serial private static final long serialVersionUID = 1L;
+
+ enum ErrorType {
+ NULL_INPUT("'null' or empty input provided"),
+ UNKNOWN_WORD("Unknown Word: "),
+ UNEXPECTED_WORD("Unexpected Word: "),
+ UNEXPECTED_WORD_AFTER_POINT("Unexpected Word (after Point): "),
+ MISSING_DECIMAL_NUMBERS("Decimal part is missing numbers."),
+ MULTIPLE_NEGATIVES("Multiple 'Negative's detected."),
+ INVALID_NEGATIVE("Incorrect 'negative' placement"),
+ INVALID_CONJUNCTION("Incorrect 'and' placement");
+
+ private final String message;
+
+ ErrorType(String message) {
+ this.message = message;
+ }
+
+ public String formatMessage(String details) {
+ return "Invalid Input. " + message + (details.isEmpty() ? "" : details);
+ }
+ }
+
+ public final ErrorType errorType;
+
+ WordsToNumberException(ErrorType errorType, String details) {
+ super(errorType.formatMessage(details));
+ this.errorType = errorType;
+ }
+
+ public ErrorType getErrorType() {
+ return errorType;
+ }
+ }
diff --git a/src/main/java/com/thealgorithms/datastructures/Node.java b/src/main/java/com/thealgorithms/datastructures/Node.java
new file mode 100644
index 000000000000..c8d0e6cb4f7d
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/Node.java
@@ -0,0 +1,32 @@
+package com.thealgorithms.datastructures;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Node {
+
+ private final T value;
+ private final List> children;
+
+ public Node(final T value) {
+ this.value = value;
+ this.children = new ArrayList<>();
+ }
+
+ public Node(final T value, final List> children) {
+ this.value = value;
+ this.children = children;
+ }
+
+ public T getValue() {
+ return value;
+ }
+
+ public void addChild(Node child) {
+ children.add(child);
+ }
+
+ public List> getChildren() {
+ return children;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/bags/Bag.java b/src/main/java/com/thealgorithms/datastructures/bags/Bag.java
index c82b9124bebc..afc3bbe40cce 100644
--- a/src/main/java/com/thealgorithms/datastructures/bags/Bag.java
+++ b/src/main/java/com/thealgorithms/datastructures/bags/Bag.java
@@ -4,23 +4,28 @@
import java.util.NoSuchElementException;
/**
- * Collection which does not allow removing elements (only collect and iterate)
+ * A generic collection that allows adding and iterating over elements but does not support
+ * element removal. This class implements a simple bag data structure, which can hold duplicate
+ * elements and provides operations to check for membership and the size of the collection.
*
- * @param - the generic type of an element in this bag
+ *
Bag is not thread-safe and should not be accessed by multiple threads concurrently.
+ *
+ * @param the type of elements in this bag
*/
-public class Bag implements Iterable {
-
- private Node firstElement; // first element of the bag
- private int size; // size of bag
+public class Bag implements Iterable {
- private static class Node {
+ private Node firstElement; // Reference to the first element in the bag
+ private int size; // Count of elements in the bag
- private Element content;
- private Node nextElement;
+ // Node class representing each element in the bag
+ private static final class Node {
+ private E content;
+ private Node nextElement;
}
/**
- * Create an empty bag
+ * Constructs an empty bag.
+ *
This initializes the bag with zero elements.
*/
public Bag() {
firstElement = null;
@@ -28,38 +33,49 @@ public Bag() {
}
/**
- * @return true if this bag is empty, false otherwise
+ * Checks if the bag is empty.
+ *
+ * @return {@code true} if the bag contains no elements; {@code false} otherwise
*/
public boolean isEmpty() {
- return firstElement == null;
+ return size == 0;
}
/**
- * @return the number of elements
+ * Returns the number of elements in the bag.
+ *
+ * @return the number of elements currently in the bag
*/
public int size() {
return size;
}
/**
- * @param element - the element to add
+ * Adds an element to the bag.
+ *
+ *
This method adds the specified element to the bag. Duplicates are allowed, and the
+ * bag will maintain the order in which elements are added.
+ *
+ * @param element the element to add; must not be {@code null}
*/
- public void add(Element element) {
- Node oldfirst = firstElement;
- firstElement = new Node<>();
- firstElement.content = element;
- firstElement.nextElement = oldfirst;
+ public void add(E element) {
+ Node newNode = new Node<>();
+ newNode.content = element;
+ newNode.nextElement = firstElement;
+ firstElement = newNode;
size++;
}
/**
- * Checks if the bag contains a specific element
+ * Checks if the bag contains a specific element.
*
- * @param element which you want to look for
- * @return true if bag contains element, otherwise false
+ *
This method uses the {@code equals} method of the element to determine membership.
+ *
+ * @param element the element to check for; must not be {@code null}
+ * @return {@code true} if the bag contains the specified element; {@code false} otherwise
*/
- public boolean contains(Element element) {
- for (Element value : this) {
+ public boolean contains(E element) {
+ for (E value : this) {
if (value.equals(element)) {
return true;
}
@@ -68,61 +84,55 @@ public boolean contains(Element element) {
}
/**
- * @return an iterator that iterates over the elements in this bag in
- * arbitrary order
+ * Returns an iterator over the elements in this bag.
+ *
+ *
The iterator provides a way to traverse the elements in the order they were added.
+ *
+ * @return an iterator that iterates over the elements in the bag
*/
- public Iterator iterator() {
+ @Override
+ public Iterator iterator() {
return new ListIterator<>(firstElement);
}
- @SuppressWarnings("hiding")
- private class ListIterator implements Iterator {
+ // Private class for iterating over elements
+ private static class ListIterator implements Iterator {
- private Node currentElement;
+ private Node currentElement;
- public ListIterator(Node firstElement) {
- currentElement = firstElement;
+ /**
+ * Constructs a ListIterator starting from the given first element.
+ *
+ * @param firstElement the first element of the bag to iterate over
+ */
+ ListIterator(Node firstElement) {
+ this.currentElement = firstElement;
}
+ /**
+ * Checks if there are more elements to iterate over.
+ *
+ * @return {@code true} if there are more elements; {@code false} otherwise
+ */
+ @Override
public boolean hasNext() {
return currentElement != null;
}
/**
- * remove is not allowed in a bag
+ * Returns the next element in the iteration.
+ *
+ * @return the next element in the bag
+ * @throws NoSuchElementException if there are no more elements to return
*/
@Override
- public void remove() {
- throw new UnsupportedOperationException();
- }
-
- public Element next() {
+ public E next() {
if (!hasNext()) {
- throw new NoSuchElementException();
+ throw new NoSuchElementException("No more elements in the bag.");
}
- Element element = currentElement.content;
+ E element = currentElement.content;
currentElement = currentElement.nextElement;
return element;
}
}
-
- /**
- * main-method for testing
- */
- public static void main(String[] args) {
- Bag bag = new Bag<>();
-
- bag.add("1");
- bag.add("1");
- bag.add("2");
-
- System.out.println("size of bag = " + bag.size());
- for (String s : bag) {
- System.out.println(s);
- }
-
- System.out.println(bag.contains(null));
- System.out.println(bag.contains("1"));
- System.out.println(bag.contains("3"));
- }
}
diff --git a/src/main/java/com/thealgorithms/datastructures/bloomfilter/BloomFilter.java b/src/main/java/com/thealgorithms/datastructures/bloomfilter/BloomFilter.java
index db85afa18c81..a2edd3db2d8e 100644
--- a/src/main/java/com/thealgorithms/datastructures/bloomfilter/BloomFilter.java
+++ b/src/main/java/com/thealgorithms/datastructures/bloomfilter/BloomFilter.java
@@ -2,35 +2,79 @@
import java.util.BitSet;
+/**
+ * A generic BloomFilter implementation for probabilistic membership checking.
+ *
+ * Bloom filters are space-efficient data structures that provide a fast way to test whether an
+ * element is a member of a set. They may produce false positives, indicating an element is
+ * in the set when it is not, but they will never produce false negatives.
+ *
+ *
+ * @param The type of elements to be stored in the Bloom filter.
+ */
public class BloomFilter {
- private int numberOfHashFunctions;
- private BitSet bitArray;
- private Hash[] hashFunctions;
+ private final int numberOfHashFunctions;
+ private final BitSet bitArray;
+ private final Hash[] hashFunctions;
- public BloomFilter(int numberOfHashFunctions, int n) {
+ /**
+ * Constructs a BloomFilter with a specified number of hash functions and bit array size.
+ *
+ * @param numberOfHashFunctions the number of hash functions to use
+ * @param bitArraySize the size of the bit array, which determines the capacity of the filter
+ * @throws IllegalArgumentException if numberOfHashFunctions or bitArraySize is less than 1
+ */
+ @SuppressWarnings("unchecked")
+ public BloomFilter(int numberOfHashFunctions, int bitArraySize) {
+ if (numberOfHashFunctions < 1 || bitArraySize < 1) {
+ throw new IllegalArgumentException("Number of hash functions and bit array size must be greater than 0");
+ }
this.numberOfHashFunctions = numberOfHashFunctions;
- hashFunctions = new Hash[numberOfHashFunctions];
- bitArray = new BitSet(n);
- insertHash();
+ this.bitArray = new BitSet(bitArraySize);
+ this.hashFunctions = new Hash[numberOfHashFunctions];
+ initializeHashFunctions();
}
- private void insertHash() {
+ /**
+ * Initializes the hash functions with unique indices to ensure different hashing.
+ */
+ private void initializeHashFunctions() {
for (int i = 0; i < numberOfHashFunctions; i++) {
- hashFunctions[i] = new Hash(i);
+ hashFunctions[i] = new Hash<>(i);
}
}
+ /**
+ * Inserts an element into the Bloom filter.
+ *
+ * This method hashes the element using all defined hash functions and sets the corresponding
+ * bits in the bit array.
+ *
+ *
+ * @param key the element to insert into the Bloom filter
+ */
public void insert(T key) {
for (Hash hash : hashFunctions) {
- int position = hash.compute(key) % bitArray.size();
+ int position = Math.abs(hash.compute(key) % bitArray.size());
bitArray.set(position);
}
}
+ /**
+ * Checks if an element might be in the Bloom filter.
+ *
+ * This method checks the bits at the positions computed by each hash function. If any of these
+ * bits are not set, the element is definitely not in the filter. If all bits are set, the element
+ * might be in the filter.
+ *
+ *
+ * @param key the element to check for membership in the Bloom filter
+ * @return {@code true} if the element might be in the Bloom filter, {@code false} if it is definitely not
+ */
public boolean contains(T key) {
for (Hash hash : hashFunctions) {
- int position = hash.compute(key) % bitArray.size();
+ int position = Math.abs(hash.compute(key) % bitArray.size());
if (!bitArray.get(position)) {
return false;
}
@@ -38,24 +82,57 @@ public boolean contains(T key) {
return true;
}
- private class Hash {
+ /**
+ * Inner class representing a hash function used by the Bloom filter.
+ *
+ * Each instance of this class represents a different hash function based on its index.
+ *
+ *
+ * @param The type of elements to be hashed.
+ */
+ private static class Hash {
- int index;
+ private final int index;
- public Hash(int index) {
+ /**
+ * Constructs a Hash function with a specified index.
+ *
+ * @param index the index of this hash function, used to create a unique hash
+ */
+ Hash(int index) {
this.index = index;
}
+ /**
+ * Computes the hash of the given key.
+ *
+ * The hash value is calculated by multiplying the index of the hash function
+ * with the ASCII sum of the string representation of the key.
+ *
+ *
+ * @param key the element to hash
+ * @return the computed hash value
+ */
public int compute(T key) {
return index * asciiString(String.valueOf(key));
}
+ /**
+ * Computes the ASCII value sum of the characters in a string.
+ *
+ * This method iterates through each character of the string and accumulates
+ * their ASCII values to produce a single integer value.
+ *
+ *
+ * @param word the string to compute
+ * @return the sum of ASCII values of the characters in the string
+ */
private int asciiString(String word) {
- int number = 0;
- for (int i = 0; i < word.length(); i++) {
- number += word.charAt(i);
+ int sum = 0;
+ for (char c : word.toCharArray()) {
+ sum += c;
}
- return number;
+ return sum;
}
}
}
diff --git a/src/main/java/com/thealgorithms/datastructures/buffers/CircularBuffer.java b/src/main/java/com/thealgorithms/datastructures/buffers/CircularBuffer.java
index 5e1c815ff9b3..b709e16fd1f6 100644
--- a/src/main/java/com/thealgorithms/datastructures/buffers/CircularBuffer.java
+++ b/src/main/java/com/thealgorithms/datastructures/buffers/CircularBuffer.java
@@ -2,56 +2,130 @@
import java.util.concurrent.atomic.AtomicInteger;
+/**
+ * The {@code CircularBuffer} class implements a generic circular (or ring) buffer.
+ * A circular buffer is a fixed-size data structure that operates in a FIFO (First In, First Out) manner.
+ * The buffer allows you to overwrite old data when the buffer is full and efficiently use limited memory.
+ * When the buffer is full, adding a new item will overwrite the oldest data.
+ *
+ * @param The type of elements stored in the circular buffer.
+ */
public class CircularBuffer {
private final Item[] buffer;
private final CircularPointer putPointer;
private final CircularPointer getPointer;
private final AtomicInteger size = new AtomicInteger(0);
+ /**
+ * Constructor to initialize the circular buffer with a specified size.
+ *
+ * @param size The size of the circular buffer.
+ * @throws IllegalArgumentException if the size is zero or negative.
+ */
public CircularBuffer(int size) {
+ if (size <= 0) {
+ throw new IllegalArgumentException("Buffer size must be positive");
+ }
// noinspection unchecked
this.buffer = (Item[]) new Object[size];
this.putPointer = new CircularPointer(0, size);
this.getPointer = new CircularPointer(0, size);
}
+ /**
+ * Checks if the circular buffer is empty.
+ * This method is based on the current size of the buffer.
+ *
+ * @return {@code true} if the buffer is empty, {@code false} otherwise.
+ */
public boolean isEmpty() {
return size.get() == 0;
}
+ /**
+ * Checks if the circular buffer is full.
+ * The buffer is considered full when its size equals its capacity.
+ *
+ * @return {@code true} if the buffer is full, {@code false} otherwise.
+ */
public boolean isFull() {
return size.get() == buffer.length;
}
+ /**
+ * Retrieves and removes the item at the front of the buffer (FIFO).
+ * This operation will move the {@code getPointer} forward.
+ *
+ * @return The item at the front of the buffer, or {@code null} if the buffer is empty.
+ */
public Item get() {
- if (isEmpty()) return null;
+ if (isEmpty()) {
+ return null;
+ }
Item item = buffer[getPointer.getAndIncrement()];
size.decrementAndGet();
return item;
}
+ /**
+ * Adds an item to the end of the buffer (FIFO).
+ * If the buffer is full, this operation will overwrite the oldest data.
+ *
+ * @param item The item to be added.
+ * @throws IllegalArgumentException if the item is null.
+ * @return {@code true} if the item was successfully added, {@code false} if the buffer was full and the item overwrote existing data.
+ */
public boolean put(Item item) {
- if (isFull()) return false;
+ if (item == null) {
+ throw new IllegalArgumentException("Null items are not allowed");
+ }
+
+ boolean wasEmpty = isEmpty();
+ if (isFull()) {
+ getPointer.getAndIncrement(); // Move get pointer to discard oldest item
+ } else {
+ size.incrementAndGet();
+ }
buffer[putPointer.getAndIncrement()] = item;
- size.incrementAndGet();
- return true;
+ return wasEmpty;
}
+ /**
+ * The {@code CircularPointer} class is a helper class used to track the current index (pointer)
+ * in the circular buffer.
+ * The max value represents the capacity of the buffer.
+ * The `CircularPointer` class ensures that the pointer automatically wraps around to 0
+ * when it reaches the maximum index.
+ * This is achieved in the `getAndIncrement` method, where the pointer
+ * is incremented and then taken modulo the maximum value (`max`).
+ * This operation ensures that the pointer always stays within the bounds of the buffer.
+ */
private static class CircularPointer {
private int pointer;
private final int max;
- public CircularPointer(int pointer, int max) {
+ /**
+ * Constructor to initialize the circular pointer.
+ *
+ * @param pointer The initial position of the pointer.
+ * @param max The maximum size (capacity) of the circular buffer.
+ */
+ CircularPointer(int pointer, int max) {
this.pointer = pointer;
this.max = max;
}
+ /**
+ * Increments the pointer by 1 and wraps it around to 0 if it reaches the maximum value.
+ * This ensures the pointer always stays within the buffer's bounds.
+ *
+ * @return The current pointer value before incrementing.
+ */
public int getAndIncrement() {
- if (pointer == max) pointer = 0;
int tmp = pointer;
- pointer++;
+ pointer = (pointer + 1) % max;
return tmp;
}
}
diff --git a/src/main/java/com/thealgorithms/datastructures/caches/LFUCache.java b/src/main/java/com/thealgorithms/datastructures/caches/LFUCache.java
index 03a1d59e1b20..f0d8ea8f7ff3 100644
--- a/src/main/java/com/thealgorithms/datastructures/caches/LFUCache.java
+++ b/src/main/java/com/thealgorithms/datastructures/caches/LFUCache.java
@@ -4,20 +4,47 @@
import java.util.Map;
/**
- * Java program for LFU Cache (https://en.wikipedia.org/wiki/Least_frequently_used)
+ * The {@code LFUCache} class implements a Least Frequently Used (LFU) cache.
+ * An LFU cache evicts the least frequently used item when the cache reaches its capacity.
+ * It maintains a mapping of keys to nodes, where each node contains the key, its associated value,
+ * and a frequency count that tracks how many times the item has been accessed. A doubly linked list
+ * is used to efficiently manage the ordering of items based on their usage frequency.
+ *
+ *
This implementation is designed to provide O(1) time complexity for both the {@code get} and
+ * {@code put} operations, which is achieved through the use of a hashmap for quick access and a
+ * doubly linked list for maintaining the order of item frequencies.
+ *
+ * @param The type of keys maintained by this cache.
+ * @param The type of mapped values.
+ *
* @author Akshay Dubey (https://github.com/itsAkshayDubey)
*/
public class LFUCache {
+ /**
+ * The {@code Node} class represents an element in the LFU cache.
+ * Each node contains a key, a value, and a frequency count.
+ * It also has pointers to the previous and next nodes in the doubly linked list.
+ */
private class Node {
-
- private K key;
+ private final K key;
private V value;
private int frequency;
private Node previous;
private Node next;
- public Node(K key, V value, int frequency) {
+ /**
+ * Constructs a new {@code Node} with the specified key, value, and frequency.
+ *
+ * @param key The key associated with this node.
+ * @param value The value stored in this node.
+ * @param frequency The frequency of usage of this node.
+ */
+ Node(K key, V value, int frequency) {
this.key = key;
this.value = value;
this.frequency = frequency;
@@ -26,67 +53,81 @@ public Node(K key, V value, int frequency) {
private Node head;
private Node tail;
- private Map map = null;
- private Integer capacity;
+ private final Map cache;
+ private final int capacity;
private static final int DEFAULT_CAPACITY = 100;
+ /**
+ * Constructs an LFU cache with the default capacity.
+ */
public LFUCache() {
- this.capacity = DEFAULT_CAPACITY;
+ this(DEFAULT_CAPACITY);
}
- public LFUCache(Integer capacity) {
+ /**
+ * Constructs an LFU cache with the specified capacity.
+ *
+ * @param capacity The maximum number of items that the cache can hold.
+ * @throws IllegalArgumentException if the specified capacity is less than or equal to zero.
+ */
+ public LFUCache(int capacity) {
+ if (capacity <= 0) {
+ throw new IllegalArgumentException("Capacity must be greater than zero.");
+ }
this.capacity = capacity;
- this.map = new HashMap<>();
+ this.cache = new HashMap<>();
}
/**
- * This method returns value present in the cache corresponding to the key passed as parameter
+ * Retrieves the value associated with the given key from the cache.
+ * If the key exists, the node's frequency is incremented, and the node is repositioned
+ * in the linked list based on its updated frequency.
*
- * @param key for which value is to be retrieved
- * @returns object corresponding to the key passed as parameter, returns null if key is
- * not present in the cache
+ * @param key The key whose associated value is to be returned.
+ * @return The value associated with the key, or {@code null} if the key is not present in the cache.
*/
public V get(K key) {
- if (this.map.get(key) == null) {
+ Node node = cache.get(key);
+ if (node == null) {
return null;
}
-
- Node node = map.get(key);
removeNode(node);
node.frequency += 1;
addNodeWithUpdatedFrequency(node);
-
return node.value;
}
/**
- * This method stores key and value in the cache
+ * Inserts or updates a key-value pair in the cache.
+ * If the key already exists, the value is updated and its frequency is incremented.
+ * If the cache is full, the least frequently used item is removed before inserting the new item.
*
- * @param key which is to be stored in the cache
- * @param value which is to be stored in the cache
+ * @param key The key associated with the value to be inserted or updated.
+ * @param value The value to be inserted or updated.
*/
public void put(K key, V value) {
- if (map.containsKey(key)) {
- Node node = map.get(key);
+ if (cache.containsKey(key)) {
+ Node node = cache.get(key);
node.value = value;
node.frequency += 1;
removeNode(node);
addNodeWithUpdatedFrequency(node);
} else {
- if (map.size() >= capacity) {
- map.remove(this.head.key);
+ if (cache.size() >= capacity) {
+ cache.remove(this.head.key); // Evict least frequently used item
removeNode(head);
}
Node node = new Node(key, value, 1);
addNodeWithUpdatedFrequency(node);
- map.put(key, node);
+ cache.put(key, node);
}
}
/**
- * This method stores the node in the cache with updated frequency
+ * Adds a node to the linked list in the correct position based on its frequency.
+ * The linked list is ordered by frequency, with the least frequently used node at the head.
*
- * @param Node node which is to be updated in the cache
+ * @param node The node to be inserted into the list.
*/
private void addNodeWithUpdatedFrequency(Node node) {
if (tail != null && head != null) {
@@ -123,9 +164,10 @@ private void addNodeWithUpdatedFrequency(Node node) {
}
/**
- * This method removes node from the cache
+ * Removes a node from the doubly linked list.
+ * This method ensures that the pointers of neighboring nodes are properly updated.
*
- * @param Node node which is to be removed in the cache
+ * @param node The node to be removed from the list.
*/
private void removeNode(Node node) {
if (node.previous != null) {
diff --git a/src/main/java/com/thealgorithms/datastructures/caches/LRUCache.java b/src/main/java/com/thealgorithms/datastructures/caches/LRUCache.java
index fcb7d975bdb4..ec39d2a6ed28 100644
--- a/src/main/java/com/thealgorithms/datastructures/caches/LRUCache.java
+++ b/src/main/java/com/thealgorithms/datastructures/caches/LRUCache.java
@@ -4,15 +4,40 @@
import java.util.Map;
/**
- * Least recently used (LRU)
- *
- * Discards the least recently used items first. This algorithm requires keeping
- * track of what was used when, which is expensive if one wants to make sure the
- * algorithm always discards the least recently used item.
- * https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)
+ * A Least Recently Used (LRU) Cache implementation.
*
- * @param key type
- * @param value type
+ *
An LRU cache is a fixed-size cache that maintains items in order of use. When the cache reaches
+ * its capacity and a new item needs to be added, it removes the least recently used item first.
+ * This implementation provides O(1) time complexity for both get and put operations.
+ *
+ *
Features:
+ *
+ *
Fixed-size cache with configurable capacity
+ *
Constant time O(1) operations for get and put
+ *
Thread-unsafe - should be externally synchronized if used in concurrent environments
+ *
Supports null values but not null keys
+ *
+ *
+ *
Implementation Details:
+ *
+ *
Uses a HashMap for O(1) key-value lookups
+ *
Maintains a doubly-linked list for tracking access order
+ *
The head of the list contains the least recently used item
+ *
The tail of the list contains the most recently used item
+ *
+ * @param the type of keys maintained by this cache
+ * @param the type of mapped values
*/
public class LRUCache {
@@ -30,6 +55,11 @@ public LRUCache(int cap) {
setCapacity(cap);
}
+ /**
+ * Returns the current capacity of the cache.
+ *
+ * @param newCapacity the new capacity of the cache
+ */
private void setCapacity(int newCapacity) {
checkCapacity(newCapacity);
for (int i = data.size(); i > newCapacity; i--) {
@@ -39,6 +69,11 @@ private void setCapacity(int newCapacity) {
this.cap = newCapacity;
}
+ /**
+ * Evicts the least recently used item from the cache.
+ *
+ * @return the evicted entry
+ */
private Entry evict() {
if (head == null) {
throw new RuntimeException("cache cannot be empty!");
@@ -50,12 +85,25 @@ private Entry evict() {
return evicted;
}
+ /**
+ * Checks if the capacity is valid.
+ *
+ * @param capacity the capacity to check
+ */
private void checkCapacity(int capacity) {
if (capacity <= 0) {
throw new RuntimeException("capacity must greater than 0!");
}
}
+ /**
+ * Returns the value to which the specified key is mapped, or null if this cache contains no
+ * mapping for the key.
+ *
+ * @param key the key whose associated value is to be returned
+ * @return the value to which the specified key is mapped, or null if this cache contains no
+ * mapping for the key
+ */
public V get(K key) {
if (!data.containsKey(key)) {
return null;
@@ -65,6 +113,11 @@ public V get(K key) {
return entry.getValue();
}
+ /**
+ * Moves the specified entry to the end of the list.
+ *
+ * @param entry the entry to move
+ */
private void moveNodeToLast(Entry entry) {
if (tail == entry) {
return;
@@ -86,6 +139,12 @@ private void moveNodeToLast(Entry entry) {
tail = entry;
}
+ /**
+ * Associates the specified value with the specified key in this cache.
+ *
+ * @param key the key with which the specified value is to be associated
+ * @param value the value to be associated with the specified key
+ */
public void put(K key, V value) {
if (data.containsKey(key)) {
final Entry existingEntry = data.get(key);
@@ -107,6 +166,11 @@ public void put(K key, V value) {
data.put(key, newEntry);
}
+ /**
+ * Adds a new entry to the end of the list.
+ *
+ * @param newEntry the entry to add
+ */
private void addNewEntry(Entry newEntry) {
if (data.isEmpty()) {
head = newEntry;
@@ -126,10 +190,10 @@ static final class Entry {
private I key;
private J value;
- public Entry() {
+ Entry() {
}
- public Entry(Entry preEntry, Entry nextEntry, I key, J value) {
+ Entry(Entry preEntry, Entry nextEntry, I key, J value) {
this.preEntry = preEntry;
this.nextEntry = nextEntry;
this.key = key;
diff --git a/src/main/java/com/thealgorithms/datastructures/caches/MRUCache.java b/src/main/java/com/thealgorithms/datastructures/caches/MRUCache.java
index 30f914968c3b..93b13e6ad654 100644
--- a/src/main/java/com/thealgorithms/datastructures/caches/MRUCache.java
+++ b/src/main/java/com/thealgorithms/datastructures/caches/MRUCache.java
@@ -4,14 +4,17 @@
import java.util.Map;
/**
- * Most recently used (MRU)
+ * Represents a Most Recently Used (MRU) Cache.
*
- * In contrast to Least Recently Used (LRU), MRU discards the most recently used
- * items first.
- * https://en.wikipedia.org/wiki/Cache_replacement_policies#Most_recently_used_(MRU)
+ * In contrast to the Least Recently Used (LRU) strategy, the MRU caching policy
+ * evicts the most recently accessed items first. This class provides methods to
+ * store key-value pairs and manage cache eviction based on this policy.
*
- * @param key type
- * @param value type
+ * For more information, refer to:
+ * MRU on Wikipedia.
+ *
+ * @param the type of keys maintained by this cache
+ * @param the type of values associated with the keys
*/
public class MRUCache {
@@ -21,40 +24,74 @@ public class MRUCache {
private int cap;
private static final int DEFAULT_CAP = 100;
+ /**
+ * Creates an MRUCache with the default capacity.
+ */
public MRUCache() {
setCapacity(DEFAULT_CAP);
}
+ /**
+ * Creates an MRUCache with a specified capacity.
+ *
+ * @param cap the maximum number of items the cache can hold
+ */
+ public MRUCache(int cap) {
+ setCapacity(cap);
+ }
+
+ /**
+ * Sets the capacity of the cache and evicts items if the new capacity
+ * is less than the current number of items.
+ *
+ * @param newCapacity the new capacity to set
+ */
private void setCapacity(int newCapacity) {
checkCapacity(newCapacity);
- for (int i = data.size(); i > newCapacity; i--) {
+ while (data.size() > newCapacity) {
Entry evicted = evict();
data.remove(evicted.getKey());
}
this.cap = newCapacity;
}
+ /**
+ * Checks if the specified capacity is valid.
+ *
+ * @param capacity the capacity to check
+ * @throws IllegalArgumentException if the capacity is less than or equal to zero
+ */
private void checkCapacity(int capacity) {
if (capacity <= 0) {
- throw new RuntimeException("capacity must greater than 0!");
+ throw new IllegalArgumentException("Capacity must be greater than 0!");
}
}
+ /**
+ * Evicts the most recently used entry from the cache.
+ *
+ * @return the evicted entry
+ * @throws RuntimeException if the cache is empty
+ */
private Entry evict() {
if (head == null) {
- throw new RuntimeException("cache cannot be empty!");
+ throw new RuntimeException("Cache cannot be empty!");
}
final Entry evicted = this.tail;
tail = evicted.getPreEntry();
- tail.setNextEntry(null);
+ if (tail != null) {
+ tail.setNextEntry(null);
+ }
evicted.setNextEntry(null);
return evicted;
}
- public MRUCache(int cap) {
- setCapacity(cap);
- }
-
+ /**
+ * Retrieves the value associated with the specified key.
+ *
+ * @param key the key whose associated value is to be returned
+ * @return the value associated with the specified key, or null if the key does not exist
+ */
public V get(K key) {
if (!data.containsKey(key)) {
return null;
@@ -64,11 +101,19 @@ public V get(K key) {
return entry.getValue();
}
+ /**
+ * Associates the specified value with the specified key in the cache.
+ * If the key already exists, its value is updated and the entry is moved to the most recently used position.
+ * If the cache is full, the most recently used entry is evicted before adding the new entry.
+ *
+ * @param key the key with which the specified value is to be associated
+ * @param value the value to be associated with the specified key
+ */
public void put(K key, V value) {
if (data.containsKey(key)) {
- final Entry exitingEntry = data.get(key);
- exitingEntry.setValue(value);
- moveEntryToLast(exitingEntry);
+ final Entry existingEntry = data.get(key);
+ existingEntry.setValue(value);
+ moveEntryToLast(existingEntry);
return;
}
Entry newEntry;
@@ -84,6 +129,11 @@ public void put(K key, V value) {
data.put(key, newEntry);
}
+ /**
+ * Adds a new entry to the cache and updates the head and tail pointers accordingly.
+ *
+ * @param newEntry the new entry to be added
+ */
private void addNewEntry(Entry newEntry) {
if (data.isEmpty()) {
head = newEntry;
@@ -96,6 +146,11 @@ private void addNewEntry(Entry newEntry) {
tail = newEntry;
}
+ /**
+ * Moves the specified entry to the most recently used position in the cache.
+ *
+ * @param entry the entry to be moved
+ */
private void moveEntryToLast(Entry entry) {
if (tail == entry) {
return;
@@ -117,17 +172,23 @@ private void moveEntryToLast(Entry entry) {
tail = entry;
}
+ /**
+ * A nested class representing an entry in the cache, which holds a key-value pair
+ * and references to the previous and next entries in the linked list structure.
+ *
+ * @param the type of the key
+ * @param the type of the value
+ */
static final class Entry {
-
private Entry preEntry;
private Entry nextEntry;
private I key;
private J value;
- public Entry() {
+ Entry() {
}
- public Entry(Entry preEntry, Entry nextEntry, I key, J value) {
+ Entry(Entry preEntry, Entry nextEntry, I key, J value) {
this.preEntry = preEntry;
this.nextEntry = nextEntry;
this.key = key;
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/GCounter.java b/src/main/java/com/thealgorithms/datastructures/crdt/GCounter.java
new file mode 100644
index 000000000000..25b01bce19f3
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/GCounter.java
@@ -0,0 +1,84 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * G-Counter (Grow-only Counter) is a state-based CRDT (Conflict-free Replicated Data Type)
+ * designed for tracking counts in a distributed and concurrent environment.
+ * Each process maintains its own counter, allowing only increments. The total count
+ * is obtained by summing individual process counts.
+ * This implementation supports incrementing, querying the total count,
+ * comparing with other G-Counters, and merging with another G-Counter
+ * to compute the element-wise maximum.
+ * (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
+ *
+ * @author itakurah (https://github.com/itakurah)
+ */
+
+class GCounter {
+ private final Map counterMap;
+ private final int myId;
+ private final int n;
+
+ /**
+ * Constructs a G-Counter for a cluster of n nodes.
+ *
+ * @param n The number of nodes in the cluster.
+ */
+ GCounter(int myId, int n) {
+ this.myId = myId;
+ this.n = n;
+ this.counterMap = new HashMap<>();
+
+ for (int i = 0; i < n; i++) {
+ counterMap.put(i, 0);
+ }
+ }
+
+ /**
+ * Increments the counter for the current node.
+ */
+ public void increment() {
+ counterMap.put(myId, counterMap.get(myId) + 1);
+ }
+
+ /**
+ * Gets the total value of the counter by summing up values from all nodes.
+ *
+ * @return The total value of the counter.
+ */
+ public int value() {
+ int sum = 0;
+ for (int v : counterMap.values()) {
+ sum += v;
+ }
+ return sum;
+ }
+
+ /**
+ * Compares the state of this G-Counter with another G-Counter.
+ *
+ * @param other The other G-Counter to compare with.
+ * @return True if the state of this G-Counter is less than or equal to the state of the other G-Counter.
+ */
+ public boolean compare(GCounter other) {
+ for (int i = 0; i < n; i++) {
+ if (this.counterMap.get(i) > other.counterMap.get(i)) {
+ return false;
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Merges the state of this G-Counter with another G-Counter.
+ *
+ * @param other The other G-Counter to merge with.
+ */
+ public void merge(GCounter other) {
+ for (int i = 0; i < n; i++) {
+ this.counterMap.put(i, Math.max(this.counterMap.get(i), other.counterMap.get(i)));
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/GSet.java b/src/main/java/com/thealgorithms/datastructures/crdt/GSet.java
new file mode 100644
index 000000000000..2b8959ed0136
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/GSet.java
@@ -0,0 +1,65 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * GSet (Grow-only Set) is a state-based CRDT (Conflict-free Replicated Data Type)
+ * that allows only the addition of elements and ensures that once an element is added,
+ * it cannot be removed. The merge operation of two G-Sets is their union.
+ * This implementation supports adding elements, looking up elements, comparing with other G-Sets,
+ * and merging with another G-Set to create a new G-Set containing all unique elements from both sets.
+ * (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
+ *
+ * @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
+ */
+
+public class GSet {
+ private final Set elements;
+
+ /**
+ * Constructs an empty G-Set.
+ */
+ public GSet() {
+ this.elements = new HashSet<>();
+ }
+
+ /**
+ * Adds an element to the G-Set.
+ *
+ * @param e the element to be added
+ */
+ public void addElement(T e) {
+ elements.add(e);
+ }
+
+ /**
+ * Checks if the given element is present in the G-Set.
+ *
+ * @param e the element to be checked
+ * @return true if the element is present, false otherwise
+ */
+ public boolean lookup(T e) {
+ return elements.contains(e);
+ }
+
+ /**
+ * Compares the G-Set with another G-Set to check if it is a subset.
+ *
+ * @param other the other G-Set to compare with
+ * @return true if the current G-Set is a subset of the other, false otherwise
+ */
+ public boolean compare(GSet other) {
+ return other.elements.containsAll(elements);
+ }
+
+ /**
+ * Merges the current G-Set with another G-Set, creating a new G-Set
+ * containing all unique elements from both sets.
+ *
+ * @param other the G-Set to merge with
+ */
+ public void merge(GSet other) {
+ elements.addAll(other.elements);
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/LWWElementSet.java b/src/main/java/com/thealgorithms/datastructures/crdt/LWWElementSet.java
new file mode 100644
index 000000000000..d33bd3ee84d9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/LWWElementSet.java
@@ -0,0 +1,126 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.time.Instant;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Last-Write-Wins Element Set (LWWElementSet) is a state-based CRDT (Conflict-free Replicated Data
+ * Type) designed for managing sets in a distributed and concurrent environment. It supports the
+ * addition and removal of elements, using timestamps to determine the order of operations. The set
+ * is split into two subsets: the add set for elements to be added and the remove set for elements
+ * to be removed. The LWWElementSet ensures that the most recent operation (based on the timestamp)
+ * wins in the case of concurrent operations.
+ *
+ * @param The type of the elements in the LWWElementSet.
+ * @author itakurah (GitHub), Niklas Hoefflin (LinkedIn)
+ * @see Conflict free
+ * replicated data type (Wikipedia)
+ * @see A comprehensive study of
+ * Convergent and Commutative Replicated Data Types
+ */
+class LWWElementSet {
+ final Map> addSet;
+ final Map> removeSet;
+
+ /**
+ * Constructs an empty LWWElementSet. This constructor initializes the addSet and removeSet as
+ * empty HashMaps. The addSet stores elements that are added, and the removeSet stores elements
+ * that are removed.
+ */
+ LWWElementSet() {
+ this.addSet = new HashMap<>();
+ this.removeSet = new HashMap<>();
+ }
+
+ /**
+ * Adds an element to the addSet with the current timestamp. This method stores the element in the
+ * addSet, ensuring that the element is added to the set with an associated timestamp that
+ * represents the time of the addition.
+ *
+ * @param key The key of the element to be added.
+ */
+ public void add(T key) {
+ addSet.put(key, new Element<>(key, Instant.now()));
+ }
+
+ /**
+ * Removes an element by adding it to the removeSet with the current timestamp. This method adds
+ * the element to the removeSet, marking it as removed with the current timestamp.
+ *
+ * @param key The key of the element to be removed.
+ */
+ public void remove(T key) {
+ removeSet.put(key, new Element<>(key, Instant.now()));
+ }
+
+ /**
+ * Checks if an element is in the LWWElementSet. An element is considered present if it exists in
+ * the addSet and either does not exist in the removeSet, or its add timestamp is later than any
+ * corresponding remove timestamp.
+ *
+ * @param key The key of the element to be checked.
+ * @return {@code true} if the element is present in the set (i.e., its add timestamp is later
+ * than its remove timestamp, or it is not in the remove set), {@code false} otherwise (i.e.,
+ * the element has been removed or its remove timestamp is later than its add timestamp).
+ */
+ public boolean lookup(T key) {
+ Element inAddSet = addSet.get(key);
+ Element inRemoveSet = removeSet.get(key);
+
+ return inAddSet != null && (inRemoveSet == null || inAddSet.timestamp.isAfter(inRemoveSet.timestamp));
+ }
+
+ /**
+ * Merges another LWWElementSet into this set. This method takes the union of both the add-sets
+ * and remove-sets from the two sets, resolving conflicts by keeping the element with the latest
+ * timestamp. If an element appears in both the add-set and remove-set of both sets, the one with
+ * the later timestamp will be retained.
+ *
+ * @param other The LWWElementSet to merge with the current set.
+ */
+ public void merge(LWWElementSet other) {
+ for (Map.Entry> entry : other.addSet.entrySet()) {
+ addSet.merge(entry.getKey(), entry.getValue(), this::resolveConflict);
+ }
+ for (Map.Entry> entry : other.removeSet.entrySet()) {
+ removeSet.merge(entry.getKey(), entry.getValue(), this::resolveConflict);
+ }
+ }
+
+ /**
+ * Resolves conflicts between two elements by selecting the one with the later timestamp. This
+ * method is used when merging two LWWElementSets to ensure that the most recent operation (based
+ * on timestamps) is kept.
+ *
+ * @param e1 The first element.
+ * @param e2 The second element.
+ * @return The element with the later timestamp.
+ */
+ private Element resolveConflict(Element e1, Element e2) {
+ return e1.timestamp.isAfter(e2.timestamp) ? e1 : e2;
+ }
+}
+
+/**
+ * Represents an element in the LWWElementSet, consisting of a key and a timestamp. This class is
+ * used to store the elements in both the add and remove sets with their respective timestamps.
+ *
+ * @param The type of the key associated with the element.
+ */
+class Element {
+ T key;
+ Instant timestamp;
+
+ /**
+ * Constructs a new Element with the specified key and timestamp.
+ *
+ * @param key The key of the element.
+ * @param timestamp The timestamp associated with the element.
+ */
+ Element(T key, Instant timestamp) {
+ this.key = key;
+ this.timestamp = timestamp;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/ORSet.java b/src/main/java/com/thealgorithms/datastructures/crdt/ORSet.java
new file mode 100644
index 000000000000..a4cc2ffdd4a6
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/ORSet.java
@@ -0,0 +1,191 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.UUID;
+
+/**
+ * ORSet (Observed-Removed Set) is a state-based CRDT (Conflict-free Replicated Data Type)
+ * that supports both addition and removal of elements. This particular implementation follows
+ * the Add-Wins strategy, meaning that in case of conflicting add and remove operations,
+ * the add operation takes precedence. The merge operation of two OR-Sets ensures that
+ * elements added at any replica are eventually observed at all replicas. Removed elements,
+ * once observed, are never reintroduced.
+ * This OR-Set implementation provides methods for adding elements, removing elements,
+ * checking for element existence, retrieving the set of elements, comparing with other OR-Sets,
+ * and merging with another OR-Set to create a new OR-Set containing all unique elements
+ * from both sets.
+ *
+ * @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
+ * @see Conflict-free_replicated_data_type
+ * @see itakurah (Niklas Hoefflin)
+ */
+
+public class ORSet {
+
+ private final Set> elements;
+ private final Set> tombstones;
+
+ /**
+ * Constructs an empty OR-Set.
+ */
+ public ORSet() {
+ this.elements = new HashSet<>();
+ this.tombstones = new HashSet<>();
+ }
+
+ /**
+ * Checks if the set contains the specified element.
+ *
+ * @param element the element to check for
+ * @return true if the set contains the element, false otherwise
+ */
+ public boolean contains(T element) {
+ return elements.stream().anyMatch(pair -> pair.getElement().equals(element));
+ }
+
+ /**
+ * Retrieves the elements in the set.
+ *
+ * @return a set containing the elements
+ */
+ public Set elements() {
+ Set result = new HashSet<>();
+ elements.forEach(pair -> result.add(pair.getElement()));
+ return result;
+ }
+
+ /**
+ * Adds the specified element to the set.
+ *
+ * @param element the element to add
+ */
+ public void add(T element) {
+ String n = prepare();
+ effect(element, n);
+ }
+
+ /**
+ * Removes the specified element from the set.
+ *
+ * @param element the element to remove
+ */
+ public void remove(T element) {
+ Set> pairsToRemove = prepare(element);
+ effect(pairsToRemove);
+ }
+
+ /**
+ * Collect all pairs with the specified element.
+ *
+ * @param element the element to collect pairs for
+ * @return a set of pairs with the specified element to be removed
+ */
+ private Set> prepare(T element) {
+ Set> pairsToRemove = new HashSet<>();
+ for (Pair pair : elements) {
+ if (pair.getElement().equals(element)) {
+ pairsToRemove.add(pair);
+ }
+ }
+ return pairsToRemove;
+ }
+
+ /**
+ * Generates a unique tag for the element.
+ *
+ * @return the unique tag
+ */
+ private String prepare() {
+ return generateUniqueTag();
+ }
+
+ /**
+ * Adds the element with the specified unique tag to the set.
+ *
+ * @param element the element to add
+ * @param n the unique tag associated with the element
+ */
+ private void effect(T element, String n) {
+ Pair pair = new Pair<>(element, n);
+ elements.add(pair);
+ elements.removeAll(tombstones);
+ }
+
+ /**
+ * Removes the specified pairs from the set.
+ *
+ * @param pairsToRemove the pairs to remove
+ */
+ private void effect(Set> pairsToRemove) {
+ elements.removeAll(pairsToRemove);
+ tombstones.addAll(pairsToRemove);
+ }
+
+ /**
+ * Generates a unique tag.
+ *
+ * @return the unique tag
+ */
+ private String generateUniqueTag() {
+ return UUID.randomUUID().toString();
+ }
+
+ /**
+ * Compares this Add-Wins OR-Set with another OR-Set to check if elements and tombstones are a subset.
+ *
+ * @param other the other OR-Set to compare
+ * @return true if the sets are subset, false otherwise
+ */
+ public boolean compare(ORSet other) {
+ Set> union = new HashSet<>(elements);
+ union.addAll(tombstones);
+
+ Set> otherUnion = new HashSet<>(other.elements);
+ otherUnion.addAll(other.tombstones);
+
+ return otherUnion.containsAll(union) && other.tombstones.containsAll(tombstones);
+ }
+
+ /**
+ * Merges this Add-Wins OR-Set with another OR-Set.
+ *
+ * @param other the other OR-Set to merge
+ */
+ public void merge(ORSet other) {
+ elements.removeAll(other.tombstones);
+ other.elements.removeAll(tombstones);
+ elements.addAll(other.elements);
+ tombstones.addAll(other.tombstones);
+ }
+
+ /**
+ * Represents a pair containing an element and a unique tag.
+ *
+ * @param the type of the element in the pair
+ */
+ public static class Pair {
+ private final T element;
+ private final String uniqueTag;
+
+ /**
+ * Constructs a pair with the specified element and unique tag.
+ *
+ * @param element the element in the pair
+ * @param uniqueTag the unique tag associated with the element
+ */
+ public Pair(T element, String uniqueTag) {
+ this.element = element;
+ this.uniqueTag = uniqueTag;
+ }
+
+ /**
+ * Gets the element from the pair.
+ *
+ * @return the element
+ */
+ public T getElement() {
+ return element;
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/PNCounter.java b/src/main/java/com/thealgorithms/datastructures/crdt/PNCounter.java
new file mode 100644
index 000000000000..53c21dcbd108
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/PNCounter.java
@@ -0,0 +1,100 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * PN-Counter (Positive-Negative Counter) is a state-based CRDT (Conflict-free Replicated Data Type)
+ * designed for tracking counts with both increments and decrements in a distributed and concurrent environment.
+ * It combines two G-Counters, one for increments (P) and one for decrements (N).
+ * The total count is obtained by subtracting the value of the decrement counter from the increment counter.
+ * This implementation supports incrementing, decrementing, querying the total count,
+ * comparing with other PN-Counters, and merging with another PN-Counter
+ * to compute the element-wise maximum for both increment and decrement counters.
+ * (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
+ *
+ * @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
+ */
+
+class PNCounter {
+ private final Map pCounter;
+ private final Map nCounter;
+ private final int myId;
+ private final int n;
+
+ /**
+ * Constructs a PN-Counter for a cluster of n nodes.
+ *
+ * @param myId The identifier of the current node.
+ * @param n The number of nodes in the cluster.
+ */
+ PNCounter(int myId, int n) {
+ this.myId = myId;
+ this.n = n;
+ this.pCounter = new HashMap<>();
+ this.nCounter = new HashMap<>();
+
+ for (int i = 0; i < n; i++) {
+ pCounter.put(i, 0);
+ nCounter.put(i, 0);
+ }
+ }
+
+ /**
+ * Increments the increment counter for the current node.
+ */
+ public void increment() {
+ pCounter.put(myId, pCounter.get(myId) + 1);
+ }
+
+ /**
+ * Increments the decrement counter for the current node.
+ */
+ public void decrement() {
+ nCounter.put(myId, nCounter.get(myId) + 1);
+ }
+
+ /**
+ * Gets the total value of the counter by subtracting the decrement counter from the increment counter.
+ *
+ * @return The total value of the counter.
+ */
+ public int value() {
+ int sumP = pCounter.values().stream().mapToInt(Integer::intValue).sum();
+ int sumN = nCounter.values().stream().mapToInt(Integer::intValue).sum();
+ return sumP - sumN;
+ }
+
+ /**
+ * Compares the state of this PN-Counter with another PN-Counter.
+ *
+ * @param other The other PN-Counter to compare with.
+ * @return True if the state of this PN-Counter is less than or equal to the state of the other PN-Counter.
+ */
+ public boolean compare(PNCounter other) {
+ if (this.n != other.n) {
+ throw new IllegalArgumentException("Cannot compare PN-Counters with different number of nodes");
+ }
+ for (int i = 0; i < n; i++) {
+ if (this.pCounter.get(i) > other.pCounter.get(i) && this.nCounter.get(i) > other.nCounter.get(i)) {
+ return false;
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Merges the state of this PN-Counter with another PN-Counter.
+ *
+ * @param other The other PN-Counter to merge with.
+ */
+ public void merge(PNCounter other) {
+ if (this.n != other.n) {
+ throw new IllegalArgumentException("Cannot merge PN-Counters with different number of nodes");
+ }
+ for (int i = 0; i < n; i++) {
+ this.pCounter.put(i, Math.max(this.pCounter.get(i), other.pCounter.get(i)));
+ this.nCounter.put(i, Math.max(this.nCounter.get(i), other.nCounter.get(i)));
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/crdt/TwoPSet.java b/src/main/java/com/thealgorithms/datastructures/crdt/TwoPSet.java
new file mode 100644
index 000000000000..c0ce17b2802b
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/crdt/TwoPSet.java
@@ -0,0 +1,84 @@
+package com.thealgorithms.datastructures.crdt;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * TwoPhaseSet (2P-Set) is a state-based CRDT (Conflict-free Replicated Data Type) designed for managing sets
+ * with support for both addition and removal operations in a distributed and concurrent environment.
+ * It combines two G-Sets (grow-only sets) - one set for additions and another set (tombstone set) for removals.
+ * Once an element is removed and placed in the tombstone set, it cannot be re-added, adhering to "remove-wins" semantics.
+ * This implementation supports querying the presence of elements, adding elements, removing elements,
+ * comparing with other 2P-Sets, and merging two 2P-Sets while preserving the remove-wins semantics.
+ * (https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type)
+ *
+ * @author itakurah (Niklas Hoefflin) (https://github.com/itakurah)
+ */
+
+public class TwoPSet {
+ private final Set setA;
+ private final Set setR;
+
+ /**
+ * Constructs an empty Two-Phase Set.
+ */
+ public TwoPSet() {
+ this.setA = new HashSet<>();
+ this.setR = new HashSet<>();
+ }
+
+ /**
+ * Checks if an element is in the set and has not been removed.
+ *
+ * @param element The element to be checked.
+ * @return True if the element is in the set and has not been removed, otherwise false.
+ */
+ public boolean lookup(T element) {
+ return setA.contains(element) && !setR.contains(element);
+ }
+
+ /**
+ * Adds an element to the set.
+ *
+ * @param element The element to be added.
+ */
+ public void add(T element) {
+ setA.add(element);
+ }
+
+ /**
+ * Removes an element from the set. The element will be placed in the tombstone set.
+ *
+ * @param element The element to be removed.
+ */
+ public void remove(T element) {
+ if (lookup(element)) {
+ setR.add(element);
+ }
+ }
+
+ /**
+ * Compares the current 2P-Set with another 2P-Set.
+ *
+ * @param otherSet The other 2P-Set to compare with.
+ * @return True if both SetA and SetR are subset, otherwise false.
+ */
+ public boolean compare(TwoPSet otherSet) {
+ return otherSet.setA.containsAll(setA) && otherSet.setR.containsAll(setR);
+ }
+
+ /**
+ * Merges the current 2P-Set with another 2P-Set.
+ *
+ * @param otherSet The other 2P-Set to merge with.
+ * @return A new 2P-Set containing the merged elements.
+ */
+ public TwoPSet merge(TwoPSet otherSet) {
+ TwoPSet mergedSet = new TwoPSet<>();
+ mergedSet.setA.addAll(this.setA);
+ mergedSet.setA.addAll(otherSet.setA);
+ mergedSet.setR.addAll(this.setR);
+ mergedSet.setR.addAll(otherSet.setR);
+ return mergedSet;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/disjointsets/DisjointSets.java b/src/main/java/com/thealgorithms/datastructures/disjointsets/DisjointSets.java
deleted file mode 100644
index cf26fce78088..000000000000
--- a/src/main/java/com/thealgorithms/datastructures/disjointsets/DisjointSets.java
+++ /dev/null
@@ -1,33 +0,0 @@
-package com.thealgorithms.datastructures.disjointsets;
-
-public class DisjointSets {
-
- public Node MakeSet(T x) {
- return new Node(x);
- }
-
- public Node FindSet(Node node) {
- if (node != node.parent) {
- node.parent = FindSet(node.parent);
- }
-
- return node.parent;
- }
-
- public void UnionSet(Node x, Node y) {
- Node nx = FindSet(x);
- Node ny = FindSet(y);
-
- if (nx == ny) {
- return;
- }
- if (nx.rank > ny.rank) {
- ny.parent = nx;
- } else if (ny.rank > nx.rank) {
- nx.parent = ny;
- } else {
- nx.parent = ny;
- ny.rank++;
- }
- }
-}
diff --git a/src/main/java/com/thealgorithms/datastructures/disjointsets/Node.java b/src/main/java/com/thealgorithms/datastructures/disjointsets/Node.java
deleted file mode 100644
index f2054331dc14..000000000000
--- a/src/main/java/com/thealgorithms/datastructures/disjointsets/Node.java
+++ /dev/null
@@ -1,13 +0,0 @@
-package com.thealgorithms.datastructures.disjointsets;
-
-public class Node