1.8 Rotate Matrix

Clock-wise rotate: matrix upside down then swap number in pairs which are symmetric by diagonal;
Anti-clock rotate: reverse matrix right->left; then do swap;

    void rotate(vector<vector<int>>& matrix) {        reverse(matrix.begin(), matrix.end());        for (int i=0; i<matrix.size(); ++i) {            for (int j=i+1; j<matrix[0].size(); ++j) {                swap(matrix[i][j], matrix[j][i]);            }        }    }    void rotate2(vector<vector<int>>& matrix){        for (int i = 0; i<matrix.size(); ++i){            reverse(matrix[i].begin(), matrix[i].end());        }        for (int i = 0; i<matrix.size(); ++i) {            for (int j = i+1; j<matrix[i].size(); ++j) {                swap(matrix[i][j], matrix[j][i]);            }        }    }