import pathlib

base_dir = pathlib.Path(__file__).parent
filename = base_dir / "day4_input.txt"

with open(base_dir / filename) as f:
    lines = f.read().splitlines()

score = 0

extra_cards = [0 for _ in lines]
n_cards = [1 for _ in lines]

for i, line in enumerate(lines):
    _, numbers = line.split(":")
    winning, have = numbers.split(" | ")

    winning_numbers = {int(n) for n in winning.split()}
    have_numbers = {int(n) for n in have.split()}

    have_winning_numbers = winning_numbers & have_numbers
    n_matches = len(have_winning_numbers)

    if n_matches:
        score += 2 ** (n_matches - 1)

    j = i + 1
    for _ in range(n_matches):
        if j >= len(lines):
            break
        n_cards[j] += n_cards[i]
        j += 1

answer_p1 = score
print(f"{answer_p1=}")

answer_p2 = sum(n_cards)
print(f"{answer_p2=}")

-- SPDX-FileCopyrightText: 2023 Jummit
--
-- SPDX-License-Identifier: GPL-3.0-or-later

local function nums(str)
	local res = {}
	for num in str:gmatch("%d+") do
		res[num] = true
	end
	return res
end

local cards = {}
local points = 0
for line in io.open("4.input"):lines() do
	local winning, have = line:match("Card%s*%d+: (.*) | (.*)")
	winning = nums(winning)
	have = nums(have)
	local first = true
	local score = 0
	local matching = 0
	for num in pairs(have) do
		if winning[num] then
			matching = matching + 1
			if first then
				first = false
				score = score + 1
			else
				score = score * 2
			end
		end
	end
	points = points + score
	table.insert(cards, {have=have, wins=matching, count=1})
end
print(points)

local cardSum = 0
for i, card in ipairs(cards) do
	cardSum = cardSum + card.count
	for n = i + 1, i + card.wins do
		cards[n].count = cards[n].count + card.count
	end
end
print(cardSum)

int main()
{
	char line[128], *rest, *tok;
	int nextra[200]={0}, nums[10], nnums;
	int p1=0,p2=0, id,val,nmatch, i;

	for (id=0; (rest = fgets(line, sizeof(line), stdin)); id++) {
		nnums = nmatch = 0;

		while ((tok = strsep(&rest, " ")) && !strchr(tok, ':'))
			;
		while ((tok = strsep(&rest, " ")) && !strchr(tok, '|'))
			if ((val = atoi(tok)))
				nums[nnums++] = val;
		while ((tok = strsep(&rest, " ")))
			if ((val = atoi(tok)))
				for (i=0; i<nnums; i++)
					nmatch += nums[i] == val;

		for (i=0; i<nmatch; i++)
			nextra[id+1+i] += nextra[id]+1;

		p1 += nmatch ? 1 << (nmatch-1) : 0;
		p2 += nextra[id]+1;
	}

	printf("%d %d\n", p1, p2);
	return 0;
}

import re

winning_number_pattern: re.Pattern = re.compile(r' +([\d ]*?) +\|')
lottery_number_pattern: re.Pattern = re.compile(r'\| +([\d ]*)')


def get_winning_numbers(line: str) -> set[str]:
    return set(winning_number_pattern.search(line).group(1).split())


def get_lottery_numbers(line: str) -> set[str]:
    return set(lottery_number_pattern.search(line).group(1).split())


def get_winnings(winning_numbers: set[str], lottery_numbers: set[str]) -> int:
    return int(2 ** (len(winning_numbers.intersection(lottery_numbers)) - 1))


def puzzle_1() -> int:
    points: int = 0
    with open('day4_scratchcards.txt', 'r', encoding='utf-8') as file:
        for line in file:
            points += get_winnings(get_winning_numbers(line), get_lottery_numbers(line))
    return points


class ScratchCard:
    def __init__(self, line: str):
        self.amount: int = 1
        self.winnings: int = len(get_winning_numbers(line).intersection(get_lottery_numbers(line)))

    def update(self, extra: int) -> None:
        self.amount = self.amount + extra

    def __radd__(self, other):
        return self.amount + other


def puzzle_2() -> int:
    scratch_card_list: list[ScratchCard] = []
    with open('day4_scratchcards.txt', 'r', encoding='utf-8') as file:
        for line in file:
            scratch_card_list.append(ScratchCard(line))

    for i, scratch_card in enumerate(scratch_card_list):
        for j in range(1, scratch_card.winnings + 1):
            try:
                scratch_card_list[i + j].update(scratch_card.amount)
            except IndexError:
                pass
    return sum(scratch_card_list)


if __name__ == '__main__':
    print(puzzle_1())
    print(puzzle_2())

Sets really came in handy for this challenge, as did recognizing that you can use powers of two to compute the points for each card. I tried using a regular expression to parse each card, but ended up just doing it manually with split :|

Numbers = set[int]
Card    = list[Numbers]

def read_cards(stream=sys.stdin) -> Iterator[Card]:
    for line in stream:
        yield [set(map(int, n.split())) for n in line.split(':')[-1].split('|')]

def main(stream=sys.stdin) -> None:
    cards  = [numbers & winning for winning, numbers in read_cards(stream)]
    points = sum(2**(len(card)-1) for card in cards if card)
    print(points)

This took me longer than I wished… I had to think about it carefully before seeing how you can just keep track of the counts of each card, and then when you get to that card, you add to its copies your current count.

def main(stream=sys.stdin) -> None:
    cards  = [numbers & winning for winning, numbers in read_cards(stream)]
    counts = defaultdict(int)

    for index, card in enumerate(cards, 1):
        counts[index] += 1
        for copy in range(index + 1, index + len(card) + 1):
            counts[copy] += counts[index]

    print(sum(counts.values()))