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Rotate Image

Problem Statement​

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

LeetCode Link

Code​

Python Code
class Solution(object):
    def rotate(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: None Do not return anything, modify matrix in-place instead.
        """
        rows, cols = len(matrix), len(matrix[0])
        for r in range(rows):
            for c in range(r, cols-r-1):
                sr, sc = r, c
                nr, nc = sc, rows-sr-1
                matrix[nr][nc], nval = matrix[sr][sc], matrix[nr][nc]
                while nr != sr or nc != sc:
                    nr, nc = nc, rows-nr-1
                    matrix[nr][nc], nval = nval, matrix[nr][nc]