66 lines
1.6 KiB
Python
66 lines
1.6 KiB
Python
from __future__ import print_function
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import math
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def zigzag( dimension):
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''' generate the zigzag indexes for a square array
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Exploiting the fact that an array is symmetrical around its
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centre
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'''
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NUMBER_INDEXES = dimension ** 2
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HALFWAY = NUMBER_INDEXES // 2
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KERNEL_ODD = dimension & 1
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xy = [0 for _ in range(NUMBER_INDEXES)]
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# start at 0,0
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ix = 0
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iy = 0
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# 'fake' that we are going up and right
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direction = 1
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# the first index is always 0, so start with the second
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# until halfway
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for i in range(1, HALFWAY + KERNEL_ODD):
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if direction > 0:
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# going up and right
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if iy == 0:
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# are at top
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ix += 1
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direction = -1
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else:
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ix += 1
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iy -= 1
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else:
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# going down and left
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if ix == 0:
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# are at left
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iy += 1
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direction = 1
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else:
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ix -= 1
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iy += 1
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# update the index position
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xy[iy * dimension + ix] = i
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# have first half, but they are scattered over the list
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# so find the zeros to replace
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for i in range(1, NUMBER_INDEXES):
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if xy[i] == 0 :
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xy[i] = NUMBER_INDEXES - 1 - xy[NUMBER_INDEXES - 1 - i]
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return xy
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def main(dim):
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zz = zigzag(dim)
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print( 'zigzag of {}:'.format(dim))
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width = int(math.ceil(math.log10(dim**2)))
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for j in range(dim):
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for i in range(dim):
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print('{:{width}}'.format(zz[j * dim + i], width=width), end=' ')
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print()
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if __name__ == '__main__':
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main(5)
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