day21.py

import collections

all_ingredients = collections.Counter()
possible_ingredients = collections.defaultdict(set)

for line in open("inputs/day21").read().splitlines():
    ingredients, allergens = line.rstrip(")").split(" (contains ")
    ingredients = ingredients.split()
    allergens = allergens.split(", ")
    all_ingredients.update(ingredients)
    for allergen in allergens:
        if not possible_ingredients[allergen]:
            possible_ingredients[allergen] = set(ingredients)
        else:
            possible_ingredients[allergen] &= set(ingredients)

fixed = {}
while possible_ingredients:
    allergen, ingredients = min(possible_ingredients.items(), key=lambda el: len(el[1]))
    fixed[allergen] = list(ingredients)[0]
    for other in possible_ingredients.values():
        other -= {fixed[allergen]}
    del possible_ingredients[allergen]

print("part1:", sum(all_ingredients[i] for i in all_ingredients if i not in fixed.values()))
print("part2:", ",".join([ingredient for _, ingredient in sorted(fixed.items())]))