Add reusable array rotation utility using reversal algorithm

src/main/java/com/thealgorithms/others/ArrayRotation.java

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+package com.thealgorithms.others;
+
+/**
+ * Array Rotation Utility
+ *
+ * Supports:
+ * 1. Left Rotation
+ * 2. Right Rotation
+ *
+ * Approach:
+ * Reversal Algorithm
+ *
+ * Time Complexity: O(n)
+ * Space Complexity: O(1)
+ */
+public final class ArrayRotation {
+
+    private ArrayRotation() {
+    }
+
+    /**
+     * Rotates the array to the right by k positions.
+     *
+     * @param nums the input array
+     * @param k    number of rotations
+     */
+    public static void rotateRight(int[] nums, int k) {
+        int n = nums.length;
+
+        if (n == 0) {
+            return;
+        }
+
+        k = k % n;
+
+        reverse(nums, 0, n - 1);
+        reverse(nums, 0, k - 1);
+        reverse(nums, k, n - 1);
+    }
+
+    /**
+     * Rotates the array to the left by k positions.
+     *
+     * @param nums the input array
+     * @param k    number of rotations
+     */
+    public static void rotateLeft(int[] nums, int k) {
+        int n = nums.length;
+
+        if (n == 0) {
+            return;
+        }
+
+        k = k % n;
+
+        reverse(nums, 0, k - 1);
+        reverse(nums, k, n - 1);
+        reverse(nums, 0, n - 1);
+    }
+
+    /**
+     * Reverses elements between start and end indices.
+     *
+     * @param nums  the input array
+     * @param start starting index
+     * @param end   ending index
+     */
+    private static void reverse(int[] nums, int start, int end) {
+        while (start < end) {
+            int temp = nums[start];
+            nums[start] = nums[end];
+            nums[end] = temp;
+
+            start++;
+            end--;
+        }
+    }
+}

src/main/java/com/thealgorithms/others/ArrayRotationTest.java

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+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class ArrayRotationTest {
+
+    @Test
+    void shouldRotateArrayRightByTwoPositions() {
+        int[] values = {1, 2, 3, 4, 5};
+
+        ArrayRotation.rotateRight(values, 2);
+
+        assertArrayEquals(new int[] {4, 5, 1, 2, 3}, values);
+    }
+
+    @Test
+    void shouldRotateArrayLeftByTwoPositions() {
+        int[] values = {1, 2, 3, 4, 5};
+
+        ArrayRotation.rotateLeft(values, 2);
+
+        assertArrayEquals(new int[] {3, 4, 5, 1, 2}, values);
+    }
+
+    @Test
+    void shouldHandleRotationGreaterThanArrayLength() {
+        int[] values = {10, 20, 30, 40};
+
+        ArrayRotation.rotateRight(values, 6);
+
+        assertArrayEquals(new int[] {30, 40, 10, 20}, values);
+    }
+
+    @Test
+    void shouldKeepSingleElementArrayUnchanged() {
+        int[] values = {99};
+
+        ArrayRotation.rotateLeft(values, 5);
+
+        assertArrayEquals(new int[] {99}, values);
+    }
+
+    @Test
+    void shouldHandleEmptyArrayWithoutErrors() {
+        int[] values = {};
+
+        ArrayRotation.rotateRight(values, 3);
+
+        assertArrayEquals(new int[] {}, values);
+    }
+
+    @Test
+    void shouldReturnOriginalArrayWhenRotationIsZero() {
+        int[] values = {7, 8, 9};
+
+        ArrayRotation.rotateLeft(values, 0);
+
+        assertArrayEquals(new int[] {7, 8, 9}, values);
+    }
+}

src/test/java/com/thealgorithms/others/ArrayRotationTest.java

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+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class ArrayRotationTest {
+
+    @Test
+    void shouldRotateArrayRightByTwoPositions() {
+        int[] values = {1, 2, 3, 4, 5};
+
+        ArrayRotation.rotateRight(values, 2);
+
+        assertArrayEquals(new int[] {4, 5, 1, 2, 3}, values);
+    }
+
+    @Test
+    void shouldRotateArrayLeftByTwoPositions() {
+        int[] values = {1, 2, 3, 4, 5};
+
+        ArrayRotation.rotateLeft(values, 2);
+
+        assertArrayEquals(new int[] {3, 4, 5, 1, 2}, values);
+    }
+
+    @Test
+    void shouldHandleRotationGreaterThanArrayLength() {
+        int[] values = {10, 20, 30, 40};
+
+        ArrayRotation.rotateRight(values, 6);
+
+        assertArrayEquals(new int[] {30, 40, 10, 20}, values);
+    }
+
+    @Test
+    void shouldKeepSingleElementArrayUnchanged() {
+        int[] values = {99};
+
+        ArrayRotation.rotateLeft(values, 5);
+
+        assertArrayEquals(new int[] {99}, values);
+    }
+
+    @Test
+    void shouldHandleEmptyArrayWithoutErrors() {
+        int[] values = {};
+
+        ArrayRotation.rotateRight(values, 3);
+
+        assertArrayEquals(new int[] {}, values);
+    }
+
+    @Test
+    void shouldReturnOriginalArrayWhenRotationIsZero() {
+        int[] values = {7, 8, 9};
+
+        ArrayRotation.rotateLeft(values, 0);
+
+        assertArrayEquals(new int[] {7, 8, 9}, values);
+    }
+ }