107 lines
2.9 KiB
Python
107 lines
2.9 KiB
Python
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#!/usr/bin/env python
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import math
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import sys
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from typing import Dict, List, Set, Tuple
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Ranges = Dict[str, Set[int]]
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Ticket = List[int]
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def parse(raw: List[str]) -> Tuple[Ranges, List[Ticket]]:
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def extract_field_info(line: str) -> Tuple[str, Set[int]]:
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field, rest = line.split(":")
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ranges: Set[int] = set()
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for r in rest.strip().split(" or "):
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lhs, rhs = r.split("-")
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ranges |= set(range(int(lhs), int(rhs) + 1))
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return field, ranges
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def parse_tickets(line: str) -> Ticket:
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return [int(i) for i in line.split(",")]
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ranges: Ranges = {}
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tickets: List[Ticket] = []
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should_parse_tickets = False
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for line in raw:
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if line == "":
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should_parse_tickets = True
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continue
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if "ticket" in line:
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continue
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if should_parse_tickets:
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tickets.append(parse_tickets(line))
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else:
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field, field_ranges = extract_field_info(line)
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ranges[field] = field_ranges
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return ranges, tickets
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def verify_mapping(possibilites: Dict[int, Set[str]]) -> None:
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for pos in possibilites.values():
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assert len(pos) == 1
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def cross_eliminate(possibilites: Dict[int, Set[str]]) -> None:
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while True:
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eliminated = False
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for pos in possibilites:
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if len(possibilites[pos]) != 1:
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continue
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for other_pos in possibilites:
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if other_pos == pos:
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continue
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if len(possibilites[other_pos] & possibilites[pos]) == 0:
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continue
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eliminated = True
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possibilites[other_pos] = possibilites[other_pos] - (possibilites[pos])
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if not eliminated:
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break
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def match_ranges(ranges: Ranges, tickets: List[Ticket]) -> Dict[int, str]:
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possibilites: Dict[int, Set[str]] = {
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i: set(ranges.keys()) for i in range(len(ranges))
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}
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def whittle_down() -> None:
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for t in tickets[1:]:
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for i, val in enumerate(t):
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for field, valid in ranges.items():
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if val in valid:
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continue
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possibilites[i].remove(field)
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whittle_down()
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cross_eliminate(possibilites)
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verify_mapping(possibilites)
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return {i: pos.pop() for i, pos in possibilites.items()}
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def solve(raw: List[str]) -> int:
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ranges, tickets = parse(raw)
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def valid(t: Ticket) -> bool:
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for val in t:
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if not any(val in r for r in ranges.values()):
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return False
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return True
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tickets = [t for i, t in enumerate(tickets) if i == 0 or valid(t)]
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mapping = match_ranges(ranges, tickets)
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return math.prod(
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tickets[0][i] for i, field in mapping.items() if "departure" in field
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)
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def main() -> None:
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input = [line.strip() for line in sys.stdin.readlines()]
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print(solve(input))
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if __name__ == "__main__":
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main()
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