aoc20-problem21.py

from functools import reduce

in_file = open('/users/andi/xworkspace/AdventOfCode-2020/input_21')
file_lines = in_file.readlines()

class Food:
    def __init__(self, input_str):
        all_tokens = input_str.strip().split('contains')
        self.allergens = [a.strip() for a in all_tokens[1][:-1].split(',')]
        self.ingredients = [a.strip() for a in all_tokens[0][:-2].split(' ')]


allergen_to_foods_map = {}
all_food_list = []
for line in file_lines:
    f = Food(line)
    all_food_list.append(f)
    for allergen in f.allergens:
        if allergen not in allergen_to_foods_map:
            allergen_to_foods_map[allergen] = [f]
        else:
            allergen_to_foods_map[allergen].append(f)

ingredients_containing_allergens_set = set()
allergens_to_ingredients_map = {}


for allergen in allergen_to_foods_map:
    # list of lists of ingredients that this allergen appears
    all_lists_of_ingredients = list(map(lambda f: f.ingredients, allergen_to_foods_map[allergen]))

    ingredients_that_might_contain_allergen = list(reduce(lambda a, b: set(a) & set(b), all_lists_of_ingredients))
    ingredients_containing_allergens_set.update(ingredients_that_might_contain_allergen)
    allergens_to_ingredients_map[allergen] = ingredients_that_might_contain_allergen


safe_ingredients = []
for food in all_food_list:
    safe_ingredients.extend(set(food.ingredients) - ingredients_containing_allergens_set)

print('Part 1: ', len(safe_ingredients))

allergen_ingredient_map = {}

while allergens_to_ingredients_map:
    for allergen in list(allergens_to_ingredients_map.keys()):
        if len(allergens_to_ingredients_map[allergen]) == 1:
            allergen_ingredient_map[allergen] = allergens_to_ingredients_map[allergen][0]
            ingredient = allergens_to_ingredients_map.pop(allergen)[0]
            for other_allergen in allergens_to_ingredients_map:
                if ingredient in allergens_to_ingredients_map[other_allergen]: allergens_to_ingredients_map[other_allergen].remove(ingredient)


canonical_dangerous_ingredient_list = []
for key in sorted(allergen_ingredient_map):
    canonical_dangerous_ingredient_list.append(allergen_ingredient_map[key])
print('Part 2: ', ','.join(canonical_dangerous_ingredient_list))