Day 21

day21/part1.py

@@ -0,0 +1,25 @@
+#!/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())
+print(sum(v for k, v in count.items() if k not in valids))
+