leetcode48

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48. Rotate Image

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]
]

Idea

tranpose firtly and mirror translate second.

Code

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class Solution:
    """
    @param matrix: a lists of integers
    @return: nothing
    """
    def rotate(self, matrix):
        # write your code here
        if matrix == None or len(matrix) == 0:
            return None
        matrix = self.transpose(matrix)
        matrix = self.mirror(matrix)
        return matrix

    def mirror(self, matrix):
        for i in range(len(matrix)):
            matrix[i].reverse()        
        return matrix
        
    def transpose(self, matrix):
        n = len(matrix)
        for i in range(n):
            for j in range(i, n):
                matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
        return matrix

Python

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# list reverse
matrix[i].reverse()
# exchange
matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]