48 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?

Solution

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

Notes
Made mistake in my first try. (Note the left and right bound of i and j for looping.)