Day 21

day21/part2.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+import re
+from collections import defaultdict
+
+lines = (x.strip() for x in open("input.txt"))
+REGEX = re.compile(r"((?:[a-z]+ )+)\(contains (.*)\)")
+
+possible_ingredients = dict()
+count = defaultdict(int)
+
+for line in lines:
+    ingredients, allergens = REGEX.match(line).groups()
+    ingredients = set(ingredients.strip().split())
+    for ing in ingredients:
+        count[ing] += 1
+    allergens = allergens.strip().split(", ")
+    for allergen in allergens:
+        if allergen in possible_ingredients:
+            possible_ingredients[allergen].intersection_update(ingredients)
+        else:
+            possible_ingredients[allergen] = set(ingredients)
+
+valids = set.union(*possible_ingredients.values())
+
+done = dict()
+while len(possible_ingredients):
+    for allergen, ingredients in possible_ingredients.copy().items():
+        if len(ingredients) == 1:
+            ing = ingredients.pop()
+            done[allergen] = ing
+            possible_ingredients.pop(allergen)
+            for ings in possible_ingredients.values():
+                ings.discard(ing)
+
+
+print(",".join(done[x] for x in sorted(done.keys())))