First clear solution for Zigzag Array by tom-tom - python coding challenges

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First solution in Clear category for Zigzag Array by tom-tom

from typing import List
from itertools import count

ORDER = slice(None, None), slice(None, None, -1)

def create_zigzag(rows: int, cols: int, start: int = 1) -> List[List[int]]:
    num = count(start)
    return [[next(num) for _ in range(cols)][ORDER[j % 2]] for j in range(rows)]

Nov. 10, 2018

Comments:

JimmyCarlos on March 31, 2019, 9:25 a.m.
This is certainly compact, but I have no idea what is happening. Could you explain how this works?

tom-tom on April 1, 2019, 8:40 p.m.
First, `num = itertools.count(start)` creates an iterator for numbers in the result grid, and calling `next(num)` gets the next number. Second, we can get a copy of the row by `row[:]`, which is `row[slice(None, None)]`, and a reversed copy of a row by `row[::-1]`, which is `row[slice(None, None, -1)]`. Finally, `[next(num) for _ in range(cols)]` makes rows, and `ORDER[j % 2]` gets one slice or another, alternatively.

JimmyCarlos on April 2, 2019, 2:55 a.m.
Thank you, that was really clear.

Alice In Wonderland

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