2018: d18: ex2: add solution

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Bruno BELANYI 2024-12-30 19:41:27 -05:00
parent 91cee79a22
commit 11b32839f4

90
2018/d18/ex2/ex2.py Executable file
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#!/usr/bin/env python
import enum
import itertools
import sys
from collections.abc import Iterator
from typing import NamedTuple
class Point(NamedTuple):
x: int
y: int
def neighbours(self) -> Iterator["Point"]:
for dx, dy in itertools.product(range(-1, 1 + 1), repeat=2):
if dx == 0 and dy == 0:
continue
yield Point(self.x + dx, self.y + dy)
class Cell(enum.StrEnum):
OPEN = "."
TREE = "|"
LUMBERYARD = "#"
def solve(input: str) -> int:
def parse(input: list[str]) -> dict[Point, Cell]:
return {
Point(x, y): Cell(c)
for x, line in enumerate(input)
for y, c in enumerate(line)
}
def step_cell(p: Point, grid: dict[Point, Cell]) -> Cell:
neighbours = (n for n in p.neighbours() if n in grid)
if grid[p] == Cell.OPEN:
trees = sum(grid[n] == Cell.TREE for n in neighbours)
return Cell.TREE if trees >= 3 else Cell.OPEN
if grid[p] == Cell.TREE:
lumberyards = sum(grid[n] == Cell.LUMBERYARD for n in neighbours)
return Cell.LUMBERYARD if lumberyards >= 3 else Cell.TREE
if grid[p] == Cell.LUMBERYARD:
continues = {Cell.TREE, Cell.LUMBERYARD} <= {grid[n] for n in neighbours}
return Cell.LUMBERYARD if continues else Cell.OPEN
assert False # Sanity check
def step(grid: dict[Point, Cell]) -> dict[Point, Cell]:
res: dict[Point, Cell] = {}
for p in map(Point._make, itertools.product(range(50), repeat=2)):
res[p] = step_cell(p, grid)
return res
def frozen(grid: dict[Point, Cell]) -> tuple[Cell, ...]:
return tuple(grid[p] for p in sorted(grid.keys()))
def thawed(hashed_grid: tuple[Cell, ...]) -> dict[Point, Cell]:
return {Point(i // 50, i % 50): c for i, c in enumerate(hashed_grid)}
def do_cycles(grid: dict[Point, Cell], end: int) -> dict[Point, Cell]:
hashed_grid = frozen(grid)
cache = {hashed_grid: 0}
t = 0
while t < end:
hashed_grid = frozen(step(thawed(hashed_grid)))
t += 1
if hashed_grid in cache:
previous_t = cache[hashed_grid]
cycle_length = t - previous_t
num_cycles = (end - t) // cycle_length
t += num_cycles * cycle_length
else:
cache[hashed_grid] = t
return thawed(hashed_grid)
grid = parse(input.splitlines())
grid = do_cycles(grid, 1000000000)
trees = sum(c == Cell.TREE for c in grid.values())
lumberyards = sum(c == Cell.LUMBERYARD for c in grid.values())
return trees * lumberyards
def main() -> None:
input = sys.stdin.read()
print(solve(input))
if __name__ == "__main__":
main()