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?

抠细节的题，题目思想如下：to implement the rotation in layers, if size is n, so there will be (int)(n / 2) layers that should be rotated. 

需要注意的是：在下面这段code里面，需要注意的是：每一层layer中 i 的取值范围是 0<= i < m - layer - 1，注意上限是m-layer-1, 不是m-layer，如果是m-layer，就会多移。。造成意想不到的结果

 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 }