103 lines
2.7 KiB
Python
103 lines
2.7 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, deque
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from collections.abc import Iterator, Sequence
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from typing import NamedTuple
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class Point(NamedTuple):
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x: int
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y: int
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def __add__(self, other):
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if not isinstance(other, Point):
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return NotImplemented
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return Point(self.x + other.x, self.y + other.y)
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def __sub__(self, other):
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if not isinstance(other, Point):
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return NotImplemented
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return Point(self.x - other.x, self.y - other.y)
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ElfMap = set[Point]
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def neighbours(p: Point) -> Iterator[Point]:
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for dx, dy in itertools.product(range(-1, 1 + 1), repeat=2):
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if dx == 0 and dy == 0:
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continue
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yield p + Point(dx, dy)
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class MoveCandidate(NamedTuple):
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dir: Point
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empties: set[Point]
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MOVES = [
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# North
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MoveCandidate(Point(-1, 0), {Point(-1, -1), Point(-1, 0), Point(-1, 1)}),
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# South
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MoveCandidate(Point(1, 0), {Point(1, -1), Point(1, 0), Point(1, 1)}),
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# West
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MoveCandidate(Point(0, -1), {Point(-1, -1), Point(0, -1), Point(1, -1)}),
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# East
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MoveCandidate(Point(0, 1), {Point(-1, 1), Point(0, 1), Point(1, 1)}),
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]
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def solve(input: list[str]) -> int:
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def to_map(input: list[str]) -> ElfMap:
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res: ElfMap = set()
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for x, line in enumerate(input):
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for y, c in enumerate(line):
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if c != "#":
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continue
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res.add(Point(x, y))
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return res
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def do_round(map: ElfMap, moves: Sequence[MoveCandidate]) -> ElfMap:
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move: dict[Point, Point] = {elf: elf for elf in map}
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dest_count: dict[Point, int] = defaultdict(int)
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# Consider destinations all at once
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for elf in map:
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if not any(n in map for n in neighbours(elf)):
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continue
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for candidate in iter(moves):
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if any((elf + delta) in map for delta in candidate.empties):
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continue
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dest = elf + candidate.dir
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move[elf] = dest
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dest_count[dest] += 1
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break
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# Only move elves that don't overlap
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res: ElfMap = set()
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for elf, dest in move.items():
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if dest_count[dest] > 1:
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res.add(elf)
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else:
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res.add(dest)
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assert len(res) == len(map) # Sanity check
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return res
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map = to_map(input)
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moves = deque(MOVES)
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i = 1
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while (new_map := do_round(map, moves)) != map:
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map = new_map
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moves.rotate(-1)
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i += 1
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return i
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def main() -> None:
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input = sys.stdin.read().splitlines()
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print(solve(input))
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if __name__ == "__main__":
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main()
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