day 7 part 1

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diff --git a/day7/day7.py b/day7/day7.py
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+"""Day 7."""
+import re
+from collections import defaultdict
+
+pattern = r"(\d+) ([a-z]+) ([a-z]+) (bag[s]?)"
+prog = re.compile(pattern)
+
+with open("input") as f:
+    sections = f.read().rstrip().split("\n")
+
+mapping = defaultdict(lambda: [])
+
+# Put bags into dict structure
+for section in sections:
+    parent, child_str = section.split(" bags contain ")
+    children = []
+    if "no other bags" not in child_str:
+        for child in child_str.replace(".", "").split(", "):
+            _, adjective, color, _ = prog.match(child).groups()
+            children.append(f"{adjective} {color}")
+    for child in children:
+        mapping[child].append(parent)
+
+# Part 1
+bags = set(mapping['shiny gold'])
+while True:
+    new_bags = bags.copy()
+    for bag in bags:
+        for new_bag in mapping[bag]:
+            new_bags.add(new_bag)
+    if len(new_bags) == len(bags):
+        print(len(bags))
+        break
+    else:
+        bags = new_bags