LeetCode Easy: 48. Rotate Image

 一、题目

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]
]

Example 2:

Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

rotate the input matrix in-place such that it becomes:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

---

 题意：给定一个矩阵，顺时针旋转90度。

 二、思路

 

 三、代码

#coding:utf-8
import numpy as np
class Solution:
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: void Do not return anything, modify matrix in-place instead.
        """
        print("old:",'\n', matrix)
        n = np.shape(matrix)[0]
        # 沿着副对角线反转
        for i in range(n):
            for j in range(n-i):
                temp = matrix[i][j]
                matrix[i][j] = matrix[n-1-j][n-1-i]
                matrix[n-1-j][n-1-i] = temp

        #沿着水平中线反转
        for i in range(n//2):
            for j in range(n):
                temp = matrix[i][j]
                matrix[i][j] = matrix[n-1-i][j]
                matrix[n-1-i][j] = temp

        print('new:','\n', matrix)

if __name__ == '__main__':
    a = [[1,2,3],
         [4,5,6],
         [7,8,9]
        ]
    ss = Solution()
    ss.rotate(a)