[leetcode]Rotate Image @ Python
原题地址:https://oj.leetcode.com/problems/rotate-image/
题意:
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?
解题思路1:首先沿着副对角线翻转一次,然后沿着水平中线翻转一次,就可以得到所要求的矩阵了。时间复杂度O(n^2),空间复杂度O(1)
class Solution: # @param matrix, a list of lists of integers # @return a list of lists of integers def rotate(self, matrix): #思路1,时间复杂度O(n^2),空间复杂度O(1) n = len(matrix) for i in range(n): for j in range(n-i): #沿着副对角线反转 matrix[i][j], matrix[n-1-j][n-1-i] = matrix[n-1-j][n-1-i], matrix[i][j] for i in range(n/2): #沿着水平中线反转 for j in range(n): matrix[i][j], matrix[n - 1 - i][j] = matrix[n - 1 - i][j], matrix[i][j] return matrix
解题思路2:先将矩阵转置,然后将矩阵的每一行翻转,就可以得到所要求的矩阵了。
reference: http://www.cnblogs.com/zuoyuan/p/3772978.html
class Solution: # @param matrix, a list of lists of integers # @return a list of lists of integers def rotate(self, matrix): n = len(matrix) for i in range(n): for j in range(i+1, n): matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j] #先将矩阵转置 for i in range(n): matrix[i].reverse() #然后将矩阵的每一行翻转 return matrix
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