58 lines
1.9 KiB
Python
58 lines
1.9 KiB
Python
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#!/usr/bin/env python
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import functools
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import itertools
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import sys
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Line = tuple[str, tuple[int, ...]]
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def solve(input: list[str]) -> int:
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def parse(input: list[str]) -> list[Line]:
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return [
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(record, tuple(map(int, groups.split(","))))
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for record, groups in map(str.split, input)
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]
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def unfold(lines: list[Line]) -> list[Line]:
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return [
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("?".join(itertools.repeat(record, 5)), groups * 5)
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for record, groups in lines
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]
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@functools.cache
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def solve_line(record: str, groups: tuple[int, ...]) -> int:
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# Empty string must have no groups left, or it's not a solve
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if len(record) == 0:
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return 1 if len(groups) == 0 else 0
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# Empty groups must not contain any broken spring, or it's not a solve
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if len(groups) == 0:
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return 1 if all(c in (".", "?") for c in record) else 0
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# Skip working springs
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if record[0] == ".":
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return solve_line(record[1:], groups)
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# Try with a '.' (and discard it directly), or a '#' for the unknown springs
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if record[0] == "?":
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return solve_line(record[1:], groups) + solve_line("#" + record[1:], groups)
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# We start with a '#', check that the group is long enough
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if len(record) < groups[0] or any(c == "." for c in record[: groups[0]]):
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return 0
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# And check that we _can_ separate the group from the next one
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if len(record) > groups[0] and record[groups[0]] == "#":
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return 0
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# Now recurse
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return solve_line(record[groups[0] + 1 :], groups[1:])
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lines = parse(input)
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lines = unfold(lines)
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return sum(solve_line(record, groups) for record, groups in lines)
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def main() -> None:
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input = sys.stdin.read().splitlines()
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print(solve(input))
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if __name__ == "__main__":
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main()
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