Add function to rotate array in-place

Implement in-place rotation of an array by k steps.

Author: argondev22

src/leetcode/189_rotate-array/20251107.ts

@@ -0,0 +1,21 @@
+/**
+ Do not return anything, modify nums in-place instead.
+ */
+export function rotate(nums: number[], k: number): void {
+    const n = nums.length;
+    k = k % n;
+
+    nums = reverse(nums, 0, n - 1);
+    nums = reverse(nums, 0, k - 1);
+    nums = reverse(nums, k, n - 1);
+};
+
+function reverse(nums: number[], startIndex: number, endIndex: number): number[] {
+    while (startIndex < endIndex) {
+        [nums[endIndex], nums[startIndex]] = [nums[startIndex], nums[endIndex]];
+
+        startIndex++;
+        endIndex--;
+    }
+    return nums;
+}