Rotate A Matrix

RotateMatrixBy90.py

# Leetcode 48 : Rotate Image

class Solution:
    def rotate90(self, matrix: List[List[int]], offset: Tuple[int, int], n: int):
        if n > 1:
            # get offset
            x, y = offset

            # rotate edges : top << left << bottom << right
            top_i, top_j = x, y
            btm_i, btm_j = x + (n - 1), y + (n - 1)
            rgt_i, rgt_j = x, y + (n - 1)
            lft_i, lft_j = x + (n - 1), y

            # avoid rotating corner twice by processing one less elem
            for k in range(n - 1):
                top = matrix[top_i][top_j + k]
                bottom = matrix[btm_i][btm_j - k]
                right = matrix[rgt_i + k][rgt_j]
                left = matrix[lft_i - k][lft_j]

                matrix[top_i][top_j + k] = left
                matrix[lft_i - k][lft_j] = bottom
                matrix[btm_i][btm_j - k] = right
                matrix[rgt_i + k][rgt_j] = top

            # rotate sub-matrix
            self.rotate90(matrix, (x + 1, y + 1), n - 2)
            
        return
      
    def rotate(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        if matrix:
            self.rotate90(matrix, (0, 0), len(matrix))
        return