96 lines
2.2 KiB
Python
Executable file
96 lines
2.2 KiB
Python
Executable file
#!/usr/bin/env python
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import dataclasses
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import itertools
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import sys
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from collections.abc import Iterator
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from typing import NamedTuple, Optional
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def sign(n: int) -> int:
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if n > 0:
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return 1
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elif n < 0:
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return -1
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return 0
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class Point(NamedTuple):
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x: int
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y: int
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@classmethod
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def from_input(cls, input: str) -> "Point":
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x, y = input.split(",")
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return cls(int(x), int(y))
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@dataclasses.dataclass
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class Line:
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points: list[Point]
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@classmethod
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def from_input(cls, input: str) -> "Line":
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points = [Point.from_input(p) for p in input.split(" -> ")]
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return cls(points)
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@property
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def all_points(self) -> set[Point]:
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res: set[Point] = set()
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for start, end in itertools.pairwise(self.points):
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dx, dy = sign(end.x - start.x), sign(end.y - start.y)
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res.add(start)
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while start != end:
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start = Point(start.x + dx, start.y + dy)
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res.add(start)
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return res
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def solve(input: list[str]) -> int:
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lines = [Line.from_input(line) for line in input]
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all_points = set.union(*(line.all_points for line in lines))
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max_height = max(p.y for p in all_points)
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def sand_candidates(p: Point) -> Iterator[Point]:
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for dx, dy in ((0, 1), (-1, 1), (1, 1)):
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yield Point(p.x + dx, p.y + dy)
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def add_sand(points: set[Point]) -> Optional[Point]:
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start = Point(500, 0)
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assert start not in points # Sanity check
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while True:
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# Steady state was reached
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if start.y >= max_height:
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return None
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viable_candidates = (p for p in sand_candidates(start) if p not in points)
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candidate = next(viable_candidates, None)
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# Sand can't fall any lower
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if candidate is None:
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break
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start = candidate
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return start
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res = 0
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while True:
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grain = add_sand(all_points)
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if grain is None:
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break
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all_points.add(grain)
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res += 1
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return res
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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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