advent-of-code/2020/d24/ex2/ex2.py

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2020-12-24 13:26:52 +01:00
#!/usr/bin/env python
import itertools
import sys
from collections import defaultdict
from copy import deepcopy
from typing import Dict, Iterator, List, Tuple
Offset = Tuple[int, int]
Grid = Dict[Offset, bool]
DELTAS = {
"nw": (0, -1),
"ne": (1, -1),
"e": (1, 0),
"se": (0, 1),
"sw": (-1, 1),
"w": (-1, 0),
}
def to_offset(path: str) -> Offset:
offset = 0, 0
i = 0
while i < len(path):
direction = path[i]
i += 1
if direction in ["s", "n"]:
direction += path[i]
i += 1
x, y = offset
dx, dy = DELTAS[direction]
offset = x + dx, y + dy
return offset
def neighbours(tile: Offset) -> Iterator[Offset]:
x, y = tile
for dx, dy in DELTAS.values():
yield x + dx, y + dy
def step(blacks: Grid) -> Grid:
to_visit = set(itertools.chain.from_iterable(neighbours(tile) for tile in blacks))
to_visit |= {tile for tile in blacks}
res: Grid = defaultdict(bool)
for tile in to_visit:
num_neighbours = sum(blacks[n] for n in neighbours(tile))
if blacks[tile]:
res[tile] = num_neighbours in (1, 2)
else:
res[tile] = num_neighbours == 2
return res
def solve(raw: List[str]) -> int:
blacks: Grid = defaultdict(bool)
for offset in map(to_offset, raw):
blacks[offset] = not blacks[offset]
for __ in range(100):
blacks = step(blacks)
return sum(blacks.values())
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()