Create 0189-rotate-array.js

Solved rotate-array in JS.

javascript/0189-rotate-array.js

@@ -0,0 +1,26 @@
+/**
+ * Two Pointers
+ * https://leetcode.com/problems/rotate-array/
+ * 
+ * Time O(n) | Space O(1)
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {void} Do not return anything, modify nums in-place instead.
+ */
+ var rotate = function(nums, k) {
+
+    // if the k exceeds the length of nums.
+    k = k % nums.length;
+
+    nums.reverse();
+    reversePortionOfArray(nums, 0, k - 1);
+    reversePortionOfArray(nums,k, nums.length - 1);
+};
+
+var reversePortionOfArray = function(nums,start,end) {
+    while(start < end) {
+        [nums[start],nums[end]] = [nums[end],nums[start]];
+        start++;
+        end--;
+    }    
+}