Advent of Code 2024 day 19 part 1

from operator import itemgetter
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, }

    while len(todo) > 0:
        part = todo.pop()
        for towel, towel_len in towels:
            if part[:towel_len] == towel:
                if part == towel:
                    return True

                todo.add(part[towel_len:])

    return False


def prune_towels(towels):
    index = 0
    while index < len(towels) and towels[index][1] > 1:
        # a towel that can be made from other towels is redundant
        if possible(towels[index][0], towels[index+1:]):
            towels.pop(index)
        else:
            index += 1


def main(towels, patterns, verbose):
    prune_towels(towels)

    total = 0
    for pattern in patterns:
        if possible(pattern, towels):
            if verbose:
                print(f'{pattern} is possible')
            total += 1
        elif verbose:
            print(f'{pattern} is not possible')

    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))