105 lines
2.6 KiB
Python
105 lines
2.6 KiB
Python
|
#!/usr/bin/env python
|
||
|
|
|
||
|
|
import copy
|
||
|
|
import sys
|
||
|
|
from collections.abc import Iterator
|
||
|
|
from typing import NamedTuple, Optional
|
||
|
|
|
||
|
|
|
||
|
|
class Point(NamedTuple):
|
||
|
|
x: int
|
||
|
|
y: int
|
||
|
|
|
||
|
|
def neighbours(self) -> Iterator["Point"]:
|
||
|
|
for dx, dy in (
|
||
|
|
(-1, 0),
|
||
|
|
(1, 0),
|
||
|
|
(0, -1),
|
||
|
|
(0, 1),
|
||
|
|
):
|
||
|
|
yield Point(self.x + dx, self.y + dy)
|
||
|
|
|
||
|
|
|
||
|
|
Trails = set[Point]
|
||
|
|
Graph = dict[Point, dict[Point, int]]
|
||
|
|
|
||
|
|
|
||
|
|
def solve(input: list[str]) -> int:
|
||
|
|
def parse(input: list[str]) -> Trails:
|
||
|
|
res: Trails = set()
|
||
|
|
|
||
|
|
for x, line in enumerate(input):
|
||
|
|
for y, c in enumerate(line):
|
||
|
|
if c == "#":
|
||
|
|
continue
|
||
|
|
res.add(Point(x, y))
|
||
|
|
|
||
|
|
return res
|
||
|
|
|
||
|
|
def to_graph(trails: Trails) -> Graph:
|
||
|
|
graph: Graph = {p: {} for p in trails}
|
||
|
|
|
||
|
|
for p in trails:
|
||
|
|
for n in p.neighbours():
|
||
|
|
if n not in trails:
|
||
|
|
continue
|
||
|
|
graph[p][n] = 1
|
||
|
|
|
||
|
|
return graph
|
||
|
|
|
||
|
|
# Remove every node which has exactly two neighbours (i.e: straight lines)
|
||
|
|
def condense_graph(graph: Graph) -> Graph:
|
||
|
|
graph = copy.deepcopy(graph)
|
||
|
|
nodes = list(graph.keys())
|
||
|
|
|
||
|
|
for n in nodes:
|
||
|
|
if len(graph[n]) != 2:
|
||
|
|
continue
|
||
|
|
(n1, d1), (n2, d2) = graph[n].items()
|
||
|
|
del graph[n1][n]
|
||
|
|
del graph[n2][n]
|
||
|
|
del graph[n]
|
||
|
|
graph[n1][n2] = d1 + d2
|
||
|
|
graph[n2][n1] = d1 + d2
|
||
|
|
|
||
|
|
return graph
|
||
|
|
|
||
|
|
def explore(graph: Graph, start: Point, end: Point) -> int:
|
||
|
|
def recurse(start: Point, seen: set[Point]) -> Optional[int]:
|
||
|
|
if start == end:
|
||
|
|
return 0
|
||
|
|
if start not in graph:
|
||
|
|
return None
|
||
|
|
next_step = (
|
||
|
|
(dist, recurse(n, seen | {n}))
|
||
|
|
for n, dist in graph[start].items()
|
||
|
|
if n not in seen
|
||
|
|
)
|
||
|
|
distances = [
|
||
|
|
(dist + steps) for dist, steps in next_step if steps is not None
|
||
|
|
]
|
||
|
|
if not distances:
|
||
|
|
return None
|
||
|
|
return max(distances)
|
||
|
|
|
||
|
|
res = recurse(start, {start})
|
||
|
|
assert res is not None # Sanity check
|
||
|
|
return res
|
||
|
|
|
||
|
|
trails = parse(input)
|
||
|
|
graph = to_graph(trails)
|
||
|
|
graph = condense_graph(graph)
|
||
|
|
start, dest = Point(0, 1), Point(len(input) - 1, len(input[0]) - 2)
|
||
|
|
assert start in graph # Sanity check
|
||
|
|
assert dest in graph # Sanity check
|
||
|
|
return explore(graph, start, dest)
|
||
|
|
|
||
|
|
|
||
|
|
def main() -> None:
|
||
|
|
input = sys.stdin.read().splitlines()
|
||
|
|
print(solve(input))
|
||
|
|
|
||
|
|
|
||
|
|
if __name__ == "__main__":
|
||
|
|
main()
|