189. Rotate Array

1.描述

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

Note:
Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

2.分析

方法一：直接计算下标，index = (i + k) % n，实现空间复杂度O(1)需要技巧。
方法二：翻转数组的前n-k个数，再翻转数组的后k个数，最后整个数组翻转。
方法三：翻转整个数组，再翻转前k个数，最后翻转数组后n-k个数。

3.代码

class Solution {
public:
    void rotate(vector& nums, int k) {
        if (nums.empty() || (k %= nums.size()) == 0) return;
        int n = nums.size();
        reverse(nums.begin(), nums.begin() + n - k);
        reverse(nums.begin() + n - k, nums.end());
        reverse(nums.begin(), nums.end());
    }
};