From d5996aed9129a7beac80585e1c755708e8d81fc0 Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Mon, 7 Dec 2020 16:58:58 +0100
Subject: [PATCH] Day 7

---
 2020/day7.py | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 2020/day7.py

diff --git a/2020/day7.py b/2020/day7.py
new file mode 100644
index 0000000..7207efb
--- /dev/null
+++ b/2020/day7.py
@@ -0,0 +1,43 @@
+import re
+from collections import defaultdict
+
+
+LINE_RE = re.compile(r"^(\w+ \w+) bags contain (.+)\.$")
+CONT_RE = re.compile(r"(\d+) (\w+ \w+) bags?")
+
+
+def main():
+    with open("day7.txt", "rt") as f:
+        lines = [line.rstrip() for line in f.readlines()]
+    rules = defaultdict(dict)
+    for line in lines:
+        match = LINE_RE.match(line)
+        subject, contained = match.groups()
+        contained = contained.split(", ")
+        for c in contained:
+            match = CONT_RE.match(c)
+            if match:
+                cn, ct = match.groups()
+                rules[subject][ct] = int(cn)
+
+    # Part 1
+    num_containers = sum(contain_shiny_gold(bag, rules) for bag in rules.copy())
+    print("Containing at least 1 shiny gold:", num_containers)
+
+    # Part 2
+    inside_shiny_gold = count_bags("shiny gold", rules) - 1
+    print("Inside shiny gold:", inside_shiny_gold)
+
+
+def contain_shiny_gold(bag, rules):
+    if "shiny gold" in rules[bag]:
+        return True
+    return any(contain_shiny_gold(b, rules) for b in rules[bag])
+
+
+def count_bags(bag, rules):
+    return sum(count_bags(b, rules) * rules[bag][b] for b in rules[bag]) + 1
+
+
+if __name__ == "__main__":
+    main()