[LeetCode] Rotate Image

A simple and in-place idea: first reverse the image in row-major order and then transpose it :-)

class Solution {
public:
    void rotate(vector<vector<int>>& matrix) {
        reverse(begin(matrix), end(matrix));
        int m = matrix.size(), n = matrix[0].size();
        for (int i = 0; i < m; i++)
            for (int j = 0; j < i; j++)
                swap(matrix[i][j], matrix[j][i]);
    }
};