70 lines
2.1 KiB
Python
70 lines
2.1 KiB
Python
"Day 4: Scratchcards"
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from __future__ import annotations
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import re
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from dataclasses import dataclass
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from functools import cached_property
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@dataclass
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class Scratchcard:
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id: int
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winning_numbers: set[int]
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your_numbers: set[int]
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id_pattern = re.compile("Card +([1-9][0-9]*)")
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@staticmethod
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def _parse_id(id_segment: str) -> int:
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id_match = Scratchcard.id_pattern.match(id_segment)
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if not id_match:
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raise ValueError("Scratchcard ID is invalid")
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return int(id_match.group(1))
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@staticmethod
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def _parse_numbers(segment: str) -> set[int]:
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try:
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return {int(n) for n in segment.strip().split(" ") if n != ""}
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except:
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raise ValueError("Scratchcard number sequence is invalid.")
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@classmethod
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def parse(cls, desc: str) -> Scratchcard:
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id_segment, _, numbers_segment = desc.partition(":")
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# fmt: off
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winning_numbers_segment, _, your_numbers_segment = numbers_segment.partition("|")
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id = cls._parse_id(id_segment)
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winning_numbers = cls._parse_numbers(winning_numbers_segment)
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your_numbers = cls._parse_numbers(your_numbers_segment)
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return Scratchcard(id, winning_numbers, your_numbers)
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@staticmethod
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def resolve_copies(cards: list[Scratchcard]) -> list[int]:
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copies = [1] * len(cards)
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for i in range(len(cards)):
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for j in range(cards[i].match_count):
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copies[i + j + 1] += copies[i]
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return copies
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@cached_property
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def match_count(self):
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matching_numbers = self.winning_numbers.intersection(self.your_numbers)
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return len(matching_numbers)
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@cached_property
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def points(self):
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return 2 ** (self.match_count - 1) if self.match_count > 0 else 0
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def solve_part_1(input: str) -> int:
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return sum(Scratchcard.parse(card_desc).points for card_desc in input.split("\n"))
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def solve_part_2(input: str) -> int:
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cards = [Scratchcard.parse(card_desc) for card_desc in input.split("\n")]
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copies = Scratchcard.resolve_copies(cards)
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return sum(copies)
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