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cleanup combination and combination test #5902

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Merged
merged 2 commits into from
Oct 26, 2024
Merged

cleanup combination and combination test #5902

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ab53016
cleanup combination and combination test
lorduke22 Oct 19, 2024
37687e0
Merge branch 'master' into cleanup_Combination
siriak Oct 26, 2024
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25 changes: 15 additions & 10 deletions src/main/java/com/thealgorithms/backtracking/Combination.java
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package com.thealgorithms.backtracking;

import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.TreeSet;
Expand All @@ -13,8 +14,6 @@ public final class Combination {
private Combination() {
}

private static int length;

/**
* Find all combinations of given array using backtracking
* @param arr the array.
Expand All @@ -23,39 +22,45 @@ private Combination() {
* @return a list of all combinations of length n. If n == 0, return null.
*/
public static <T> List<TreeSet<T>> 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<TreeSet<T>> result = new LinkedList<>();
backtracking(array, 0, new TreeSet<T>(), result);
backtracking(array, n, 0, new TreeSet<T>(), 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 <T> the type of elements in the array.
*/
private static <T> void backtracking(T[] arr, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
if (index + length - currSet.size() > arr.length) {
private static <T> void backtracking(T[] arr, int n, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
if (index + n - currSet.size() > arr.length) {
return;
}
if (length - 1 == currSet.size()) {
if (currSet.size() == n - 1) {
for (int i = index; i < arr.length; i++) {
currSet.add(arr[i]);
result.add((TreeSet<T>) 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]);
}
}
Expand Down
22 changes: 21 additions & 1 deletion src/test/java/com/thealgorithms/backtracking/CombinationTest.java
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Original file line number Diff line number Diff line change
@@ -1,17 +1,28 @@
package com.thealgorithms.backtracking;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import org.junit.jupiter.api.Test;

public class CombinationTest {

@Test
void testNegativeElement() {
Integer[] array = {1, 2};
assertThrows(IllegalArgumentException.class, () -> { Combination.combination(array, -1); });
}

@Test
void testNoElement() {
List<TreeSet<Integer>> result = Combination.combination(new Integer[] {1, 2}, 0);
assertTrue(result == null);
assertNotNull(result);
assertEquals(0, result.size());
}

@Test
Expand All @@ -28,4 +39,13 @@ void testLengthTwo() {
assertTrue(arr[0] == 1);
assertTrue(arr[1] == 2);
}

@Test
void testCombinationsWithStrings() {
List<TreeSet<String>> result = Combination.combination(new String[] {"a", "b", "c"}, 2);
assertEquals(3, result.size());
assertTrue(result.contains(new TreeSet<>(Set.of("a", "b"))));
assertTrue(result.contains(new TreeSet<>(Set.of("a", "c"))));
assertTrue(result.contains(new TreeSet<>(Set.of("b", "c"))));
}
}