94 lines
2.4 KiB
Python
Executable file
94 lines
2.4 KiB
Python
Executable file
#!/usr/bin/env python
|
|
|
|
import enum
|
|
import sys
|
|
from collections.abc import Iterator
|
|
from typing import NamedTuple, Optional
|
|
|
|
|
|
class Point(NamedTuple):
|
|
x: int
|
|
y: int
|
|
|
|
|
|
class Cell(enum.StrEnum):
|
|
PATH = "."
|
|
NORTH_SLOPE = "^"
|
|
SOUTH_SLOPE = "v"
|
|
WEST_SLOPE = "<"
|
|
EAST_SLOPE = ">"
|
|
|
|
def neighbours(self) -> Iterator[Point]:
|
|
match self:
|
|
case self.PATH:
|
|
yield from (
|
|
Point(-1, 0),
|
|
Point(1, 0),
|
|
Point(0, -1),
|
|
Point(0, 1),
|
|
)
|
|
case self.NORTH_SLOPE:
|
|
yield Point(-1, 0)
|
|
case self.SOUTH_SLOPE:
|
|
yield Point(1, 0)
|
|
case self.WEST_SLOPE:
|
|
yield Point(0, -1)
|
|
case self.EAST_SLOPE:
|
|
yield Point(0, 1)
|
|
|
|
def apply(self, pos: Point) -> Iterator[Point]:
|
|
for dx, dy in self.neighbours():
|
|
yield Point(pos.x + dx, pos.y + dy)
|
|
|
|
|
|
Trails = dict[Point, Cell]
|
|
|
|
|
|
def solve(input: list[str]) -> int:
|
|
def parse(input: list[str]) -> Trails:
|
|
res: Trails = {}
|
|
|
|
for x, line in enumerate(input):
|
|
for y, c in enumerate(line):
|
|
if c == "#":
|
|
continue
|
|
res[Point(x, y)] = Cell(c)
|
|
|
|
return res
|
|
|
|
def explore(trails: Trails, start: Point, dest: Point) -> int:
|
|
def recurse(start: Point, seen: set[Point]) -> Optional[int]:
|
|
if start == dest:
|
|
return 0
|
|
if start not in trails:
|
|
return None
|
|
next_step = (
|
|
recurse(n, seen | {n})
|
|
for n in trails[start].apply(start)
|
|
if n not in seen
|
|
)
|
|
distances = [dist for dist in next_step if dist is not None]
|
|
if not distances:
|
|
return None
|
|
return max(distances) + 1
|
|
|
|
res = recurse(start, {start})
|
|
assert res is not None # Sanity check
|
|
return res
|
|
|
|
trails = parse(input)
|
|
start, dest = Point(0, 1), Point(len(input) - 1, len(input[0]) - 2)
|
|
assert start in trails # Sanity check
|
|
assert dest in trails # Sanity check
|
|
sys.setrecursionlimit(10_000)
|
|
return explore(trails, start, dest)
|
|
|
|
|
|
def main() -> None:
|
|
input = sys.stdin.read().splitlines()
|
|
print(solve(input))
|
|
|
|
|
|
if __name__ == "__main__":
|
|
main()
|