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：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。

代码：

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]
        for i in range(n):
            matrix[i].reverse()
        return matrix