Rotate Image <leetcode>

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

思路：首先左右翻转，然后按照左下，右上对角线翻转，代码如下：

 1 class Solution {
 2 public:
 3     void rotate(vector<vector<int> > &matrix) {
 4         int n=matrix.size();
 5         if(n==1)  return;
 6         for(int i=0;i<n;i++)
 7         {
 8             for(int j=0;j<n/2;j++)
 9             {
10                 swap(matrix[i][j],matrix[i][n-j-1]);
11
12             }
13         }
14         for(int i=0;i<n;i++)
15         {
16             for(int j=0;j<n-i;j++)
17             {
18                 swap(matrix[i][j],matrix[n-j-1][n-i-1]);
19             }
20         }
21     }
22 };