189.Rotate Array

题目

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

Follow up:

Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem. Could you do it in-place with O(1) extra space

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 <= 2 * 104
-231 <= nums[i] <= 231 - 1
0 <= k <= 105

https://leetcode-cn.com/problems/rotate-array

题目大意

旋转数组

解题思路

• 旋转K次，遍历K * len 次，时间复杂度 O(n^2) 无法通过
• 翻转一次，再对0-((k%len) - 1)翻转 在对(k % len) - (len -1)翻转

代码实现

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {void} Do not return anything, modify nums in-place instead.
 */
var rotate = function(nums, k) {
    var len = nums.length;
    var t = k % len;
    reverse(nums, 0, len - 1);
    reverse(nums, 0, t - 1);
    reverse(nums, t, len - 1);
};
 
function reverse(arr, from, to) {
    while (to > from) {
        var temp = arr[from];
        arr[from] = arr[to];
        arr[to] = temp;
        to--;
        from++;
    }
}