Rotate Image

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?

分析：先沿对角线进行对折，然后沿水平中线对折。

运行时间：6ms

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