91 lines
2.8 KiB
Python
91 lines
2.8 KiB
Python
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#!/usr/bin/env python
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import enum
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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
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class Point(NamedTuple):
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x: int
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y: int
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def neighbours(self) -> 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 Point(self.x + dx, self.y + dy)
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class Cell(enum.StrEnum):
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OPEN = "."
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TREE = "|"
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LUMBERYARD = "#"
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def solve(input: str) -> int:
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def parse(input: list[str]) -> dict[Point, Cell]:
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return {
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Point(x, y): Cell(c)
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for x, line in enumerate(input)
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for y, c in enumerate(line)
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}
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def step_cell(p: Point, grid: dict[Point, Cell]) -> Cell:
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neighbours = (n for n in p.neighbours() if n in grid)
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if grid[p] == Cell.OPEN:
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trees = sum(grid[n] == Cell.TREE for n in neighbours)
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return Cell.TREE if trees >= 3 else Cell.OPEN
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if grid[p] == Cell.TREE:
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lumberyards = sum(grid[n] == Cell.LUMBERYARD for n in neighbours)
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return Cell.LUMBERYARD if lumberyards >= 3 else Cell.TREE
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if grid[p] == Cell.LUMBERYARD:
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continues = {Cell.TREE, Cell.LUMBERYARD} <= {grid[n] for n in neighbours}
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return Cell.LUMBERYARD if continues else Cell.OPEN
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assert False # Sanity check
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def step(grid: dict[Point, Cell]) -> dict[Point, Cell]:
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res: dict[Point, Cell] = {}
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for p in map(Point._make, itertools.product(range(50), repeat=2)):
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res[p] = step_cell(p, grid)
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return res
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def frozen(grid: dict[Point, Cell]) -> tuple[Cell, ...]:
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return tuple(grid[p] for p in sorted(grid.keys()))
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def thawed(hashed_grid: tuple[Cell, ...]) -> dict[Point, Cell]:
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return {Point(i // 50, i % 50): c for i, c in enumerate(hashed_grid)}
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def do_cycles(grid: dict[Point, Cell], end: int) -> dict[Point, Cell]:
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hashed_grid = frozen(grid)
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cache = {hashed_grid: 0}
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t = 0
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while t < end:
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hashed_grid = frozen(step(thawed(hashed_grid)))
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t += 1
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if hashed_grid in cache:
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previous_t = cache[hashed_grid]
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cycle_length = t - previous_t
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num_cycles = (end - t) // cycle_length
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t += num_cycles * cycle_length
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else:
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cache[hashed_grid] = t
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return thawed(hashed_grid)
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grid = parse(input.splitlines())
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grid = do_cycles(grid, 1000000000)
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trees = sum(c == Cell.TREE for c in grid.values())
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lumberyards = sum(c == Cell.LUMBERYARD for c in grid.values())
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return trees * lumberyards
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def main() -> None:
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input = sys.stdin.read()
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print(solve(input))
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if __name__ == "__main__":
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main()
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