Rotate Image

 1 class Solution {
 2 public:
 3     void rotate(vector<vector<int>>& matrix) {
 4         if (matrix.empty() || matrix[0].empty()) return;
 5         
 6         int n = matrix.size();
 7         // first swap matrix[i][j] with matrix[m - 1 - i][j]
 8         for (int i = 0; i < n / 2; i++) {
 9             for (int j = 0; j < n; j++)
10                 swap(matrix[i][j], matrix[n - 1 - i][j]);
11         }
12         // swap matrix[i][j] with [j][i]
13         for (int i = 0; i < n; i++) {
14             for (int j = 0; j < i; j++) 
15                 swap(matrix[i][j], matrix[j][i]);
16         }
17     }
18 };