Added RangeInSortedArray.java in Java/Misc

TheAlgorithms · AzadN · Nov 4, 2020 · Nov 4, 2020 · Nov 4, 2020 · Nov 4, 2020
commit ffbc3b1bead0cde256e91f8b613412e399db46d9
diff --git a/Misc/RangeInSortedArray.java b/Misc/RangeInSortedArray.java
@@ -0,0 +1,82 @@
+package Misc;
+
+import java.util.*;
+
+public class RangeInSortedArray {
+
+    public static void main(String[] args) {
+        // Testcases
+        assert Arrays.equals(sortedRange(new int[] {1, 2, 3, 3, 3, 4, 5}, 3), new int[] {2, 4});
+        assert Arrays.equals(sortedRange(new int[] {1, 2, 3, 3, 3, 4, 5}, 4), new int[] {5, 5});
+        assert Arrays.equals(sortedRange(new int[] {0, 1, 2}, 3), new int[] {-1, -1});
+    }
+
+    // Get the 1st and last occurrence index of a number 'key' in a non-decreasing array 'nums'
+    // Gives [-1, -1] in case element doesn't exist in array
+    public static int[] sortedRange(int[] nums, int key) {
+        int[] range = new int[] {-1, -1};
+        alteredBinSearchIter(nums, key, 0, nums.length - 1, range, true);
+        alteredBinSearchIter(nums, key, 0, nums.length - 1, range, false);
+        return range;
+    }
+
+    // Recursive altered binary search which searches for leftmost as well as rightmost occurrence of
+    // 'key'
+    public static void alteredBinSearch(
+            int[] nums, int key, int left, int right, int[] range, boolean goLeft) {
+        if (left > right) return;
+        int mid = (left + right) / 2;
+        if (nums[mid] > key) alteredBinSearch(nums, key, left, mid - 1, range, goLeft);
+        else if (nums[mid] < key) alteredBinSearch(nums, key, mid + 1, right, range, goLeft);
+        else {
+            if (goLeft) {
+                if (mid == 0 || nums[mid - 1] != key) range[0] = mid;
+                else alteredBinSearch(nums, key, left, mid - 1, range, goLeft);
+            } else {
+                if (mid == nums.length - 1 || nums[mid + 1] != key) range[1] = mid;
+                else alteredBinSearch(nums, key, mid + 1, right, range, goLeft);
+            }
+        }
+    }
+
+    // Iterative altered binary search which searches for leftmost as well as rightmost occurrence of
+    // 'key'
+    public static void alteredBinSearchIter(
+            int[] nums, int key, int left, int right, int[] range, boolean goLeft) {
+        while (left <= right) {
+            int mid = (left + right) / 2;
+            if (nums[mid] > key) right = mid - 1;
+            else if (nums[mid] < key) left = mid + 1;
+            else {
+                if (goLeft) {
+                    if (mid == 0 || nums[mid - 1] != key) {
+                        range[0] = mid;
+                        return;
+                    } else right = mid - 1;
+                } else {
+                    if (mid == nums.length - 1 || nums[mid + 1] != key) {
+                        range[1] = mid;
+                        return;
+                    } else left = mid + 1;
+                }
+            }
+        }
+    }
+
+    public static int getCountLessThan(int[] nums, int key) {
+        return getLessThan(nums, key, 0, nums.length - 1);
+    }
+
+    public static int getLessThan(int[] nums, int key, int left, int right) {
+        int count = 0;
+        while (left <= right) {
+            int mid = (left + right) / 2;
+            if (nums[mid] > key) right = mid - 1;
+            else if (nums[mid] <= key) {
+                count = mid + 1; // Atleast mid+1 elements exist which are <= key
+                left = mid + 1;
+            }
+        }
+        return count;
+    }
+}