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