[Solved] 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.

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Question

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:

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

Example 2:

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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

Python Solution

class Solution:
    def rotate(self, matrix):
        """
        Do not return anything, modify matrix in-place instead.
        """
        l = len(matrix)
        if l==1 or l==0:
            return
        for i in range(l//2):
            for j in range(i,l-1):
                matrix[i][j],matrix[j][l-1] = matrix[j][l-1], matrix[i][j]
                matrix[i][j],matrix[l-1][l-1-j+i] = matrix[l-1][l-1-j+i], matrix[i][j]
                matrix[i][j],matrix[l-1-j+i][i] = matrix[l-1-j+i][i], matrix[i][j]
            l-=1
        return
        

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