day4

day4_part1.py

#!/usr/bin/env python3

from typing import Set


def str_to_set(numbers: str) -> Set[int]:
    return set(int(x) for x in numbers.strip().split(" ") if x)


ans = 0
with open("input.txt") as f:
    for line in f:
        _, parts = line.split(":")
        winning_numbers, player_numbers = parts.split("|")
        winning_numbers = str_to_set(winning_numbers)
        player_numbers = str_to_set(player_numbers)
        common = len(winning_numbers & player_numbers)
        if common > 0:
            ans += 1 << (common - 1)

print(ans)

day4_part2.py

#!/usr/bin/env python3

import re
from collections import defaultdict
from typing import Set

CARD_RE = re.compile(r"^Card\s+(\d+)")

def str_to_set(numbers: str) -> Set[int]:
    return set(int(x) for x in numbers.strip().split(" ") if x)


cards = defaultdict(int)
max_card_id = 0
with open("input.txt") as f:
    for line in f:
        card, parts = line.split(":")
        card_id = int(CARD_RE.match(card).group(1))
        max_card_id = max(max_card_id, card_id)

        cards[card_id] += 1

        winning_numbers, player_numbers = parts.split("|")
        winning_numbers = str_to_set(winning_numbers)
        player_numbers = str_to_set(player_numbers)
        common = len(winning_numbers & player_numbers)
        while common > 0:
            cards[card_id + common] += cards[card_id]
            common -= 1

print(sum(value for key, value in cards.items() if key <= max_card_id))