advent-of-code/2021/d09/ex2/ex2.py

62 lines
1.7 KiB
Python
Executable file

#!/usr/bin/env python
import itertools
import sys
from typing import Iterator, List, Tuple
HeightMap = List[List[int]]
Point = Tuple[int, int]
def solve(input: List[str]) -> int:
height_map = [[int(c) for c in line] for line in input]
def neighbours_of(point: Point) -> Iterator[Point]:
for dx, dy in (-1, 0), (1, 0), (0, -1), (0, 1):
x, y = point[0] + dx, point[1] + dy
if x < 0 or x >= len(height_map):
continue
if y < 0 or y >= len(height_map[0]):
continue
yield x, y
def is_low_point(point: Point) -> bool:
for neighbour in neighbours_of(point):
if height_map[neighbour[0]][neighbour[1]] <= height_map[point[0]][point[1]]:
return False
return True
def explore_bassin(point: Point) -> int:
to_be_seen = set(neighbours_of(point))
explored = {point}
bassin = {point}
while len(to_be_seen) > 0:
new = to_be_seen.pop()
explored.add(new)
if height_map[new[0]][new[1]] == 9:
continue
bassin.add(new)
for neighbour in neighbours_of(new):
if neighbour in explored:
continue
to_be_seen.add(neighbour)
return len(bassin)
points = [(x, y) for x in range(len(height_map)) for y in range(len(height_map[0]))]
low_points = filter(is_low_point, points)
bassin_sizes = sorted(map(explore_bassin, low_points), reverse=True)
return bassin_sizes[0] * bassin_sizes[1] * bassin_sizes[2]
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()