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?

/*

First reverse up to down, then swap the symmetry.

time:O(n^2), space:O(1)

*/

public class Solution {

    public void rotate(int[][] matrix) {

        if (matrix == null || matrix.length == 0) {

            return;

        }

        if (matrix[0] == null || matrix[0].length == 0) {

            return;

        }

        int m = matrix.length;

        int n = matrix[0].length;

        for (int i = 0; i < m / 2; i++) {

            for (int j = 0; j < n; j++) {

                swap(matrix, i, j, m - 1 - i, j);

            }

        }

        for (int i = 0; i < m; i++) {

            for (int j = i; j < n; j++) {

                swap(matrix, i, j, j, i);

            }

        }

    }

    public void swap(int[][] matrix, int a, int b, int c, int d) {

        int tmp = matrix[a][b];

        matrix[a][b] = matrix[c][d];

        matrix[c][d] = tmp;

    }

}