leetcode48 Rotate Image

 1 """
 2 You are given an n x n 2D matrix representing an image.
 3 Rotate the image by 90 degrees (clockwise).
 4 Note:
 5 You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
 6 Example 1:
 7 Given input matrix =
 8 [
 9   [1,2,3],
10   [4,5,6],
11   [7,8,9]
12 ],
13 rotate the input matrix in-place such that it becomes:
14 [
15   [7,4,1],
16   [8,5,2],
17   [9,6,3]
18 ]
19 Example 2:
20 Given input matrix =
21 [
22   [ 5, 1, 9,11],
23   [ 2, 4, 8,10],
24   [13, 3, 6, 7],
25   [15,14,12,16]
26 ],
27 rotate the input matrix in-place such that it becomes:
28 [
29   [15,13, 2, 5],
30   [14, 3, 4, 1],
31   [12, 6, 8, 9],
32   [16, 7,10,11]
33 ]
34 """
35 class Solution:
36     def rotate(self, matrix):
37         """
38         Do not return anything, modify matrix in-place instead.
39         """
40         matrix.reverse() #[::-1]
41         for i in range(len(matrix)):
42             for j in range(i): #注意这里是range(i),交换一遍就行
43                 matrix[j][i], matrix[i][j] = matrix[i][j], matrix[j][i]