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  1. Prepare
  2. Algorithms
  3. Implementation
  4. Matrix Layer Rotation
  5. Discussions

Matrix Layer Rotation

  • alex1269
     + 0 comments

    Python implementation within time constraints. The idea is to get a linear list for a given circle and set the starting pointer to where it should be after rotating N times instead of rotating each circle N times. 

    def rotate(matrix: list[list[int]], count: int):
    m = len(matrix)
    n = len(matrix[0])

    # given circle 
    for r in range(min(m, n) // 2):
        max_x = n - r - 1
        max_y = m - r - 1
        # flattening the circle
        circle = (
            # top
            [matrix[r][i] for i in range(r, max_x + 1)] +
            # right
            [matrix[y][max_x] for y in range(r + 1, max_y)] +
            # bottom
            [matrix[max_y][i] for i in range(max_x, r - 1, -1)] + 
            # left
            [matrix[y][r] for y in range(max_y - 1, r, -1)]
        )
        length = len(circle)
        pointer = count % length
        idx = pointer
        
        # top
        for i in range(r, max_x + 1):    
            matrix[r][i] = circle[idx]
            idx = idx + 1 if idx < length - 1 else 0
        
        # right
        for i in range(r + 1, max_y):            
            matrix[i][max_x] = circle[idx]
            idx = idx + 1 if idx < length - 1 else 0
        
        # bottom   
        for i in range(max_x + 1, r, -1):            
            matrix[max_y][i - 1] = circle[idx]
            idx = idx + 1 if idx < length - 1 else 0
        
        # left
        for i in range(max_y, r + 1, -1):            
            matrix[i - 1][r] = circle[idx]
            idx = idx + 1 if idx < length - 1 else 0
    

def matrixRotation(matrix, r):    
    rotate(matrix, r)

    for row in matrix:
        print(*row)