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

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        int n = matrix.size();
        for(int i = 0; i < n; i++){
            for(int j = 0; j < n - i; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[n - 1 - j][n - 1 - i];
                matrix[n - 1 - j][n - 1 - i] = temp;
            }
        }
        for(int i = 0; i < n / 2; i++){
            for(int j = 0; j < n; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[n - 1 - i][j];
                matrix[n - 1 - i][j] = temp;
            }
        }
    }
};