LeetCode: Rotate Image 解题报告

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?

 

SOLUTION 1:

我们可以把它当作多个嵌套的环来处理，一环加一环。从外环处理到内环。为了方便处理各种下标，我们定义top, bottom, left, right来限制环的左右上下边界。

1. 令tmp = 上边界

2. 上边等于左边元素

3. 左边等于下边元素

4. 下边等于右边元素

5. 右边等于上边元素（tmp）

使用n来记录每一圈的边长。一圈进行4次操作，每次操作移动n - 1个元素即可。

 1 public class Solution {

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

 3         if (matrix == null || matrix.length == 0 

 4            || matrix[0].length == 0) {

 5             return;       

 6         }

 7         

 8         int n = matrix.length;

 9         int top = 0, down = n - 1, left = 0, right = n - 1;

10         

11         while (n > 1) {

12             for (int i = 0; i < n - 1; i++) {

13                 int tmp = matrix[top][left + i];

14                 // 另上边等于左边

15                 matrix[top][left + i] = matrix[down - i][left];

16                 

17                 // 另左边等于下边

18                 matrix[down - i][left] = matrix[down][right - i];

19                 

20                 // 另下边等于右边

21                 matrix[down][right - i] = matrix[top + i][right];

22                 

23                 // 另右边等于上边

24                 matrix[top + i][right] = tmp;

25             }

26             top++;

27             right--;

28             left++;

29             down--;

30             

31             n -= 2;

32         }

33         

34         return;

35     }

36 }

View Code

 

GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/array/Rotate.java