48. Rotate Image 旋转矩阵的通用方法

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?

class Solution {
public:
/*
 * clockwise rotate
 * first reverse up to down, then swap the symmetry 
 * 1 2 3     7 8 9     7 4 1
 * 4 5 6  => 4 5 6  => 8 5 2
 * 7 8 9     1 2 3     9 6 3
*/
    void rotate(vector>& m) {
        reverse(m.begin(), m.end());
        int rows = m.size(), cols = m[0].size();
        if(rows == 0) return;
        for(int i = 0; i < rows - 1; i++ )
            for(int j = i + 1; j < cols; j++)
                swap(m[i][j], m[j][i]);
        
    }
};