Rotate Image - LeetCode 48, Array/Math/Matrix

You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).

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:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2:

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

 

Constraints:

• n == matrix.length == matrix[i].length
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

풀이

행렬의 전치(transpose) 후 열 순서 뒤집기

class Solution(object):
    def rotate(self, matrix):
        matrix_len = len(matrix)
        for ix, x in enumerate(matrix):
            for iy, y in enumerate(x):
                if iy <= ix:
                    continue
                matrix[ix][iy] = matrix[iy][ix]
                matrix[iy][ix] = y

        for col in range(matrix_len // 2):
            for row in range(matrix_len):
                temp = matrix[row][col]
                matrix[row][col] = matrix[row][matrix_len - 1 - col]
                matrix[row][matrix_len - 1 - col] = temp

        print(matrix)
        return matrix