Advent of Code 2024 day 19 part 2

from operator import itemgetter
from collections import defaultdict
from argparse import ArgumentParser, FileType


def parse_towels(line):
    return sorted(((towel, len(towel)) for towel in line.split(', ')),
                  key=itemgetter(1), reverse=True)


def parse_patterns(src):
    return [line for line in src.splitlines() if line != '']


def parse(src):
    towels, patterns = src.split('\n\n', 1)
    return parse_towels(towels), parse_patterns(patterns)


def possible(pattern, towels):
    todo = {pattern, }
    counts = defaultdict(int, {pattern: 1})

    while len(todo) > 0:
        part = max(todo, key=len)
        todo.remove(part)
        for towel, towel_len in towels:
            if part[:towel_len] == towel:
                new_part = part[towel_len:]
                counts[new_part] += counts[part]

                if new_part != '':
                    todo.add(new_part)

    return counts['']


def main(towels, patterns, verbose):
    total = 0
    for pattern in patterns:
        result = possible(pattern, towels)
        if verbose:
            print(f'{pattern} can be made in {result} ways')
        total += result

    return total


arg_parser = ArgumentParser()
arg_parser.add_argument('src', type=FileType('r'))
arg_parser.add_argument('-v', '--verbose', action='store_true')

if __name__ == '__main__':
    args = arg_parser.parse_args()
    print(main(*parse(args.src.read()), args.verbose))