advent-of-code/2020/d16/ex2/ex2.py

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2020-12-16 10:11:06 +01:00
#!/usr/bin/env python
import math
import sys
from typing import Dict, List, Set, Tuple
Ranges = Dict[str, Set[int]]
Ticket = List[int]
def parse(raw: List[str]) -> Tuple[Ranges, List[Ticket]]:
def extract_field_info(line: str) -> Tuple[str, Set[int]]:
field, rest = line.split(":")
ranges: Set[int] = set()
for r in rest.strip().split(" or "):
lhs, rhs = r.split("-")
ranges |= set(range(int(lhs), int(rhs) + 1))
return field, ranges
def parse_tickets(line: str) -> Ticket:
return [int(i) for i in line.split(",")]
ranges: Ranges = {}
tickets: List[Ticket] = []
should_parse_tickets = False
for line in raw:
if line == "":
should_parse_tickets = True
continue
if "ticket" in line:
continue
if should_parse_tickets:
tickets.append(parse_tickets(line))
else:
field, field_ranges = extract_field_info(line)
ranges[field] = field_ranges
return ranges, tickets
def verify_mapping(possibilites: Dict[int, Set[str]]) -> None:
for pos in possibilites.values():
assert len(pos) == 1
def cross_eliminate(possibilites: Dict[int, Set[str]]) -> None:
while True:
eliminated = False
for pos in possibilites:
if len(possibilites[pos]) != 1:
continue
for other_pos in possibilites:
if other_pos == pos:
continue
if len(possibilites[other_pos] & possibilites[pos]) == 0:
continue
eliminated = True
possibilites[other_pos] = possibilites[other_pos] - (possibilites[pos])
if not eliminated:
break
def match_ranges(ranges: Ranges, tickets: List[Ticket]) -> Dict[int, str]:
possibilites: Dict[int, Set[str]] = {
i: set(ranges.keys()) for i in range(len(ranges))
}
def whittle_down() -> None:
for t in tickets[1:]:
for i, val in enumerate(t):
for field, valid in ranges.items():
if val in valid:
continue
possibilites[i].remove(field)
whittle_down()
cross_eliminate(possibilites)
verify_mapping(possibilites)
return {i: pos.pop() for i, pos in possibilites.items()}
def solve(raw: List[str]) -> int:
ranges, tickets = parse(raw)
def valid(t: Ticket) -> bool:
for val in t:
if not any(val in r for r in ranges.values()):
return False
return True
tickets = [t for i, t in enumerate(tickets) if i == 0 or valid(t)]
mapping = match_ranges(ranges, tickets)
return math.prod(
tickets[0][i] for i, field in mapping.items() if "departure" in field
)
def main() -> None:
input = [line.strip() for line in sys.stdin.readlines()]
print(solve(input))
if __name__ == "__main__":
main()