Rotate Array

题目来源
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.

第一种最简单的方法呢，是直接创建另一个数组，然后rotate之后再赋值回去。
如下：

class Solution {
public:
    void rotate(vector& nums, int k) {
        int n = nums.size();
        vector nums2(n, 0);
        k = k % n;
        for (int i=0; i

这种方法需要O(n)的空间和复杂度。想想怎么改进，想了想，反转3次就可以了，代码如下，只需要O(1)的空间。

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

需要注意的是reverse的开始指的是第一个元素，结束指的是结束元素的下一个位置。