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?

 1 public class Solution {
 2     public void rotate(int[][] matrix) {
 3         int m = matrix.length;
 4         if (m == 0) return; 
 5         for (int layer = 0; layer < m / 2; layer++) {
 6             for (int i = layer; i < m - layer - 1; i++) {
 7                 int temp = matrix[layer][i]; //store up elements
 8                 matrix[layer][i] = matrix[m-1-i][layer]; // up is substituted by left
 9                 matrix[m-1-i][layer] = matrix[m-1-layer][m-1-i]; // left is substituted by down
10                 matrix[m-1-layer][m-1-i] = matrix[i][m-1-layer]; // down is substitued by right
11                 matrix[i][m-1-layer] = temp; // right is substituted by stored elements
12             }
13         }
14     }
15 }