189. Rotate Array

Problem

Tags: Array, Math, Two Pointers

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

Input: nums = [-1,-100,3,99], k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

Constraints:

• 1 <= nums.length <= 10^5
• -2^31 <= nums[i] <= 2^31 - 1
• 0 <= k <= 10^5

Follow up:

• Try to come up with as many solutions as you can. There are at least three different ways to solve this problem.
• Could you do it in-place with O(1) extra space?

Code

JS

// 189. Rotate Array (3/23/53714)
// Runtime: 104 ms (71.87%) Memory: 50.08 MB (94.87%) 

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {void} Do not return anything, modify nums in-place instead.
 */
function rotate(nums, k) {
    const steps = k % nums.length;
    if (steps === 0) return;

    reverse(0, nums.length - 1);
    reverse(0, steps - 1);
    reverse(steps, nums.length - 1);

    function reverse(start, end) {
        while (start < end) {
            [nums[start], nums[end]] = [nums[end], nums[start]];
            start++;
            end--;
        }
    }
}