106 lines
3.2 KiB
Python
106 lines
3.2 KiB
Python
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#!/usr/bin/env python
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import itertools
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import sys
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from typing import NamedTuple, Optional
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class AlmanacMapLine(NamedTuple):
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dest_start: int
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source_start: int
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map_len: int
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class AlmanacMap(NamedTuple):
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lines: list[AlmanacMapLine]
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def map(self, input: int) -> int:
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for l in self.lines:
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if input < l.source_start:
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continue
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if (l.source_start + l.map_len) <= input:
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continue
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return l.dest_start + (input - l.source_start)
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return input
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Almanac = dict[str, tuple[str, AlmanacMap]]
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SeedRanges = list[tuple[int, int]]
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def solve(input: str) -> int:
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def parse_almanac_map_line(line: str) -> AlmanacMapLine:
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dest_start, source_start, map_len = map(int, line.split(" "))
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return AlmanacMapLine(dest_start, source_start, map_len)
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def parse_almanac_map(lines: list[str]) -> tuple[str, str, AlmanacMap]:
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source, dest = lines[0].split(" ")[0].split("-")[::2]
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map_lines = [parse_almanac_map_line(line) for line in lines[1:]]
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return source, dest, AlmanacMap(map_lines)
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def parse_almanac(paragraphs: list[str]) -> Almanac:
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res: Almanac = {}
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for raw_map in paragraphs:
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source, dest, map = parse_almanac_map(raw_map.splitlines())
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res[source] = dest, map
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return res
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def parse(input: str) -> tuple[SeedRanges, Almanac]:
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raw_seeds, *raw_almanac = input.split("\n\n")
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parsed_seed = [int(n) for n in raw_seeds.removeprefix("seeds: ").split(" ")]
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seed_ranges = list(zip(parsed_seed[::2], parsed_seed[1::2]))
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return seed_ranges, parse_almanac(raw_almanac)
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# Each input is piped to exactly one output type, so we can reverse it easily
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def reverse_almanac(almanac: Almanac) -> Almanac:
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def reverse_map_line(line: AlmanacMapLine) -> AlmanacMapLine:
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return AlmanacMapLine(
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dest_start=line.source_start,
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source_start=line.dest_start,
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map_len=line.map_len,
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)
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def reverse_map(map: AlmanacMap) -> AlmanacMap:
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return AlmanacMap([reverse_map_line(line) for line in map.lines])
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reversed: Almanac = {}
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for source, (dest, map) in almanac.items():
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reversed[dest] = source, reverse_map(map)
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return reversed
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def lowest_location(seeds: SeedRanges, inverse_almanac: Almanac) -> int:
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def recurse(input: int, input_type: str) -> Optional[int]:
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if input_type == "seed":
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for start, length in seeds:
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if start <= input and input < (start + length):
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return input
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return None
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new_input_type, map = inverse_almanac[input_type]
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return recurse(map.map(input), new_input_type)
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for location in itertools.count():
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if recurse(location, "location") is not None:
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return location
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assert False # Sanity check
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seeds, almanac = parse(input)
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return lowest_location(seeds, reverse_almanac(almanac))
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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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