Rotate Array

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.

思路：想出尽可能多的方法，这里先写一种，以后再想其他的。

方法1：时间复杂度O(n)，空间复杂度O(n - k % n)。

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        vector<int> tem;
        int n = nums.size();
        k %= n;
        for (int i = 0; i < n - k; i++)
            tem.push_back(nums[i]);
        for (int i = n - k; i < n; i++)
            nums[i - n + k] = nums[i];
        for (int i = k; i < n; i++)
            nums[i] = tem[i - k];
    }
};

 方法2：将前n-k个数反转，将后k个数反转，将所有数反转。时间复杂度O(n)，空间复杂度O(1).

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