Leetcode: Rotate Image

最新推荐文章于 2017-06-03 09:19:48 发布

原创最新推荐文章于 2017-06-03 09:19:48 发布 · 363 阅读

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本文探讨了如何在不使用额外内存的情况下，将二维矩阵旋转90度，并详细解释了两种实现方法：第一种通过计算对应索引进行旋转，第二种则是先左右翻转再进行对称交换。

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Question

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?

Analysis

There are two methods
1. calculate the corresponding indexes
2. reverse left to right , then swap the symmetry.

The second way is tricky.

Solution

class Solution:
    # @param {integer[][]} matrix
    # @return {void} Do not return anything, modify matrix in-place instead.
    def rotate(self, matrix):
        if len(matrix)==0 or len(matrix[0])==0:
            return None

        n = len(matrix)
        for col in range(n/2):
            for row in range(n):
                matrix[row][col],matrix[row][n-1-col] = matrix[row][n-1-col], matrix[row][col]

        for row in range(n):
            for col in range(n-row):
                matrix[row][col],matrix[n-1-col][n-1-row] = matrix[n-1-col][n-1-row],matrix[row][col]