1 /*
 2     Basically, divide the array into 4 along the diagonals, 
 3     then for each element in the top quadrant, place it into
 4     the slot 90 degrees cw, and the old 90 in 180 degrees cw,
 5     and the old 180 in 270 degrees , and the old 270 in
 6     the original place.
 7  */
 8 class Solution {
 9 public:
10     void rotate(vector<vector<int> > &matrix) {
11         int n = (int)matrix.size();
12         for (int i = 0; i < n/2; i++) for (int j = i; j < n-1-i; j++) {
13                 swap(matrix[i][j], matrix[j][n-1-i]);
14                 swap(matrix[i][j], matrix[n-1-i][n-1-j]);
15                 swap(matrix[i][j], matrix[n-1-j][i]);
16         }
17     }
18 };