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