189. 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.

[show hint]

Related problem: Reverse Words in a String II

自己写的需要o(k)的置换空间

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        int tmp;
        int n = nums.size();
        if (n <= 1) return ;
        k = k % n;
        vector<int> v(k);
        for (int i = n - 1; i > n - k - 1; --i) {
            v[n - 1 - i] = nums[i]; 
        }
        for (int i = n - 1; i >= 0; --i) {
            if (i - k >= 0) nums[i] = nums[i - k];
            else nums[i] = v[k - i - 1];
        }
    }
};

其他人的写法。真的是太妙了

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        int n = nums.size();
        if (n <= 1) return ;
        k = k%n;
        reverse(nums.begin(), nums.end());
        reverse(nums.begin(), nums.begin() + k);
        reverse(nums.begin() + k, nums.end());
    }
};

reverse()函数处理参数左闭右开