advent-of-code/2021/d13/ex1/ex1.py

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2021-12-13 14:25:44 +01:00
#!/usr/bin/env python
import itertools
import sys
from copy import deepcopy
from typing import Iterable, List, Tuple, cast
Paper = List[List[bool]]
Instruction = Tuple[str, int]
def solve(input: List[str]) -> int:
def transpose(paper: Paper) -> Paper:
return cast(Paper, list(zip(*paper)))
def fold_along_y(paper: Paper, y: int) -> Paper:
assert not any(paper[y]) # Sanity check
assert y >= len(paper) // 2 # Ensure that we can actually fold the paper
paper = deepcopy(paper)
for i, j in zip(itertools.count(y, -1), range(y, len(paper))):
paper[i] = [(dot_i or dot_j) for dot_i, dot_j in zip(paper[i], paper[j])]
paper = paper[:y]
return paper
def fold_along_x(paper: Paper, x: int) -> Paper:
return transpose(fold_along_y(transpose(paper), x))
def do_folds(paper: Paper, instructions: Iterable[Instruction]) -> Paper:
for axis, n in instructions:
if axis == "x":
paper = fold_along_x(paper, n)
elif axis == "y":
paper = fold_along_y(paper, n)
else:
assert False # Sanity check
return paper
def parse() -> Tuple[Paper, List[Instruction]]:
paper_part = itertools.takewhile(lambda s: s != "", input)
fold_part = itertools.islice(
itertools.dropwhile(lambda s: s != "", input), 1, None
)
points = {(int(x), int(y)) for x, y in map(lambda s: s.split(","), paper_part)}
folds = [
(axis[-1], int(n)) for axis, n in map(lambda s: s.split("="), fold_part)
]
width, height = max(p[0] for p in points), max(p[1] for p in points)
paper = [
[(x, y) in points for x in range(width + 1)] for y in range(height + 1)
]
return paper, folds
paper, instructions = parse()
return sum(itertools.chain.from_iterable(do_folds(paper, instructions[:1])))
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()