LeetCode48. Rotate Image（思路及python解法）

最新推荐文章于 2020-08-09 19:55:17 发布

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最新推荐文章于 2020-08-09 19:55:17 发布

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分类专栏： Python LeetCode

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本文介绍了一种在不使用额外空间的情况下，将2D矩阵顺时针旋转90度的算法。首先，通过交换元素实现矩阵沿主对角线的翻转，接着再进行水平翻转，最终完成矩阵的旋转。

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You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Note:

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.

Example 1:

Given input matrix = 
[
  [1,2,3],
  [4,5,6],
  [7,8,9]
],

rotate the input matrix in-place such that it becomes:
[
  [7,4,1],
  [8,5,2],
  [9,6,3]
]

将2D矩阵顺时针旋转90度。

可以先将矩阵沿对角线做对称变换

[[1, 4, 7],

[2, 5, 8],

[3, 6, 9]]

然后沿水平方向做轴对称即可。

class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        n = len(matrix)
        
        for i in range(n):
            for j in range(i+1):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
        for i in range(n):
            for j in range(int(n/2)):
                matrix[i][j],matrix[i][n-j-1]= matrix[i][n-j-1], matrix[i][j]