2023: d04: ex2: add solution

2023/d04/ex2/ex2.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python
+
+import dataclasses
+import sys
+
+
+@dataclasses.dataclass
+class Card:
+    win_nums: set[int]
+    nums: set[int]
+    copies: int = 1
+
+
+# The input is in order without skipping, but just in case...
+Cards = dict[int, Card]
+
+
+def solve(input: list[str]) -> int:
+    def parse_nums(nums: str) -> set[int]:
+        return {int(n) for n in nums.split(" ") if n != ""}
+
+    # This does *not* expect the "Card <int>:" bit
+    def parse_card(card: str) -> Card:
+        win_nums, nums = card.split("|")
+        return Card(
+            win_nums=parse_nums(win_nums),
+            nums=parse_nums(nums),
+        )
+
+    def parse_line(line: str) -> tuple[int, Card]:
+        card_id, card = line.split(": ")
+        return int(card_id.removeprefix("Card")), parse_card(card)
+
+    def parse(input: list[str]) -> Cards:
+        parsed = map(parse_line, input)
+        return {id: card for id, card in parsed}
+
+    def score(card: Card) -> int:
+        actual_win_nums = card.nums & card.win_nums
+        return len(actual_win_nums)
+
+    cards = parse(input)
+    for i, card in cards.items():
+        winnings = score(card)
+        for n in range(1, winnings + 1):
+            cards[i + n].copies += card.copies
+
+    return sum(card.copies for card in cards.values())
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()