Cleanup day 4 solution

advent_of_code/scratchcards.py

@@ -0,0 +1,69 @@
+"Day 4: Scratchcards"
+
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass
+from functools import cached_property
+
+
+@dataclass
+class Scratchcard:
+    id: int
+    winning_numbers: set[int]
+    your_numbers: set[int]
+
+    id_pattern = re.compile("Card +([1-9][0-9]*)")
+
+    @staticmethod
+    def _parse_id(id_segment: str) -> int:
+        id_match = Scratchcard.id_pattern.match(id_segment)
+        if not id_match:
+            raise ValueError("Scratchcard ID is invalid")
+        return int(id_match.group(1))
+
+    @staticmethod
+    def _parse_numbers(segment: str) -> set[int]:
+        try:
+            return {int(n) for n in segment.strip().split(" ") if n != ""}
+        except:
+            raise ValueError("Scratchcard number sequence is invalid.")
+
+    @classmethod
+    def parse(cls, desc: str) -> Scratchcard:
+        id_segment, _, numbers_segment = desc.partition(":")
+        # fmt: off
+        winning_numbers_segment, _, your_numbers_segment = numbers_segment.partition("|")
+
+        id = cls._parse_id(id_segment)
+        winning_numbers = cls._parse_numbers(winning_numbers_segment)
+        your_numbers = cls._parse_numbers(your_numbers_segment)
+
+        return Scratchcard(id, winning_numbers, your_numbers)
+
+    @staticmethod
+    def resolve_copies(cards: list[Scratchcard]) -> list[int]:
+        copies = [1] * len(cards)
+        for i in range(len(cards)):
+            for j in range(cards[i].match_count):
+                copies[i + j + 1] += copies[i]
+        return copies
+
+    @cached_property
+    def match_count(self):
+        matching_numbers = self.winning_numbers.intersection(self.your_numbers)
+        return len(matching_numbers)
+
+    @cached_property
+    def points(self):
+        return 2 ** (self.match_count - 1) if self.match_count > 0 else 0
+
+
+def solve_part_1(input: str) -> int:
+    return sum(Scratchcard.parse(card_desc).points for card_desc in input.split("\n"))
+
+
+def solve_part_2(input: str) -> int:
+    cards = [Scratchcard.parse(card_desc) for card_desc in input.split("\n")]
+    copies = Scratchcard.resolve_copies(cards)
+    return sum(copies)