Leetcode[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

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

分析： (使用三次反转)利用$ba=(b^r)^r(a^r)^r=(a^rb^r)^r$，先分别反转a、b，最后再对所有元素进行一次反转。此算法读写内存各约2*n次。

结论：将数组按照k值分成左右两部分，右边k个，左边n-k个，然后先将左右两部分各自翻转，再将整个数组整体翻转，即可得到结果。

Code（c++）：

class Solution
{
    public:
        void swap(int * s1,int * s2)
        {
            int temp = *s1;
            *s1 = *s2;
            *s2 = temp;
        }

        void rotate(vector<int> & nums,int k)
        {
            int n = nums.size();
            int left = n - (k % n);
            for(int i = 0,j = left - 1;i < j;i++,j--)
                swap(&nums[i],&nums[j]);
            for(int i = left,j = n - 1;i < j;i++,j--)
                swap(&nums[i],&nums[j]);
            for(int i = 0,j = n - 1;i < j;i++,j--)
                swap(&nums[i],&nums[j]);
        }
};