[LeetCode] Rotate Image

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?

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