LeetCode Rotate Image

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