48. Rotate Image

Обновлено: 2024-03-25
1 мин

LeetCode problem

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:

Example LeetCode 48. Rotate Image

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

Example 2:

Example LeetCode 48. Rotate Image

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]]

Idea

class Solution:
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        l = 0
        r = len(matrix) - 1

        while l < r:
            for i in range(r-l):  # for not only "corners"
                t = l
                b = r
                top_left = matrix[t][l + i]
                matrix[t][l + i] = matrix[b - i][l]  # top left=bottom left
                matrix[b - i][l] = matrix[b][r - i]  # bottom left=bottom right
                matrix[b][r - i] = matrix[t+i][r]  # bottom right=top right
                matrix[t + i][r] = top_left         # top right=top left

            l += 1
            r -= 1

Approach 2: Reverse

class Solution:
  def rotate(self, matrix: List[List[int]]) -> None:
    matrix.reverse()

    for i in range(len(matrix)):
      for j in range(i + 1, len(matrix)):
        matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]

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