90 lines
2.4 KiB
Python
90 lines
2.4 KiB
Python
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#!/usr/bin/env python
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import sys
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from typing import Iterator, 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 (
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(-1, 0),
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(1, 0),
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(0, -1),
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(0, 1),
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):
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yield Point(self.x + dx, self.y + dy)
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def solve(input: str) -> int:
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def parse(input: list[str]) -> dict[Point, str]:
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return {
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Point(x, y): c for x, line in enumerate(input) for y, c in enumerate(line)
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}
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def find_plots(garden: dict[Point, str]) -> list[set[Point]]:
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res: list[set[Point]] = []
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visited: set[Point] = set()
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for p, plant in garden.items():
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if p in visited:
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continue
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plot: set[Point] = set()
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to_visit = {p}
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while to_visit:
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p = to_visit.pop()
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visited.add(p)
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plot.add(p)
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assert garden[p] == plant # Sanity check
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for n in p.neighbours():
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if garden.get(n) != plant:
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continue
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if n in visited:
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continue
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to_visit.add(n)
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res.append(plot)
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return res
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def count_corners(plot: set[Point]) -> int:
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def corners(p: Point) -> int:
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res = 0
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for dx, dy in (
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(-1, -1),
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(1, 1),
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(-1, 1),
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(1, -1),
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):
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diag = Point(p.x + dx, p.y + dy)
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vert = Point(p.x + dx, p.y)
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hori = Point(p.x, p.y + dy)
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# Both sides are out: an outside corner
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if vert not in plot and hori not in plot:
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res += 1
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# Both sides are in, diagonal is out: an inside corner
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if vert in plot and hori in plot and diag not in plot:
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res += 1
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return res
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return sum(corners(p) for p in plot)
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def fence_price(plot: set[Point]) -> int:
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area = len(plot)
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# Number of sides is equal to number of corners
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sides = count_corners(plot)
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return area * sides
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garden = parse(input.splitlines())
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plots = find_plots(garden)
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return sum(map(fence_price, plots))
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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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