a common method to rotate the image

 /*
  * clockwise rotate
  * first reverse up to down, then swap the symmetry
  * 1 2 3     7 8 9     7 4 1
  * 4 5 6  => 4 5 6  => 8 5 2
  * 7 8 9     1 2 3     9 6 3
 */
 void rotate(vector<vector<int> > &matrix) {
     reverse(matrix.begin(), matrix.end());
     for (int i = ; i < matrix.size(); ++i) {
         for (int j = i + ; j < matrix[i].size(); ++j)
             swap(matrix[i][j], matrix[j][i]);
     }
 }

 /*
  * anticlockwise rotate
  * first reverse left to right, then swap the symmetry
  * 1 2 3     3 2 1     3 6 9
  * 4 5 6  => 6 5 4  => 2 5 8
  * 7 8 9     9 8 7     1 4 7
 */
 void anti_rotate(vector<vector<int> > &matrix) {
     for (auto vi : matrix) reverse(vi.begin(), vi.end());
     for (int i = ; i < matrix.size(); ++i) {
         for (int j = i + ; j < matrix[i].size(); ++j)
             swap(matrix[i][j], matrix[j][i]);
     }
 }

这边有一个题目链接可以练习。