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

Matrix Layer Rotation

  • Hzzkygcs
     + 1 comment

    One of the idea is by extracting to straps, rotate it, and combine it back as a matrix.

    For the last one, combining it back is quite tedious, so I personally prefer to utilize classes (in-place assignments / reference-assignment) so that I dont need to deal the last one (combine it back)

    For the strap example, it should be: matrix (height=5, width=4):

    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

    There will be 2 straps: [1, 5, 9, 13, 17, 18, 19, 20, 16, 12, 8, 4, 3, 2] and the second one: [6, 10, 14, 15, 11, 7, ]

    class Value():
    def __init__(self, val):
        self.val = val
    
    def set(self, new_val):
        self.val = new_val
        
    def __str__(self):
        return str(f"{self.val}")

    def __repr__(self):
        return str(f"{self.val:2d}")


def matrixRotation(matrix, r):
    h = len(matrix)
    w = len(matrix[0])
    
    matrix = [   # convert to reference-based values
        [
            Value(col)
            for col in row
        ]
        for row in matrix
    ]
    # max number of straps. indexes means strap
    num_of_indexes = min(h,w) // 2  

    for index in range(num_of_indexes):
        extracted = extract(matrix, index)
        extracted_render = [x.val for x in extracted]
        r_mod = r % len(extracted_render)
        for i in range(len(extracted)):
            extracted[i].val = extracted_render[i-r_mod]
						
		# combine back process. But because we use classes/references, 
		# dont need to do extra complex things here. Just print as usual
    for row in matrix:
        print(" ".join(map(str, row)))
        
    

def extract(matrix, dia_index):  # extract strap arrays by strap-index 
    h = len(matrix)
    w = len(matrix[0])
    ret = []
    for y in range(dia_index+0, h-dia_index):  # from top-left to bottom
        ret.append(matrix[y][dia_index])
    for x in range(dia_index+1, w-dia_index):  # from bottom-left to right (except the first item, already included by for-loop above)
        ret.append(matrix[-dia_index-1][x])
    for y in range(h-1 - 1 - dia_index, dia_index - 1, -1):  # from bottom-right to top (except the first item)
        ret.append(matrix[y][-dia_index-1])
    for x in range(w-1 - 1 - dia_index, dia_index, -1):  # from top-right to left   (except first and last item)
        ret.append(matrix[dia_index][x])
    return ret