Rotate Image [LeetCode]

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

Solution:

     void rotate(vector<vector<int> > &matrix) {
         int n = matrix.size();
         for(int i = ; i < n / ; i ++) {
             for(int j = i; j < n -  - i; j ++){
                 int tmp = matrix[i][j];
                 matrix[i][j] = matrix[n -  - j][i];
                 matrix[n -  - j][i] = matrix[n -  - i][n -  - j];
                 matrix[n -  - i][n -  - j] = matrix[j][n -  - i];
                 matrix[j][n -  - i] = tmp;
             }
         }
     }