From e2dd1e03066c593a1df19190c4c72f27ea9714dd Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 25 Dec 2020 15:20:51 +0100
Subject: Add day 7

---
 07/b.rb | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 07/b.rb

(limited to '07/b.rb')

diff --git a/07/b.rb b/07/b.rb
new file mode 100644
index 0000000..2a63e10
--- /dev/null
+++ b/07/b.rb
@@ -0,0 +1,36 @@
+rules = {}
+contains = {}
+File.readlines('input.txt').each do |line|
+  line.chomp!
+  bag, contents = line.split 'bags contain' 
+  bag.strip!
+  rules[bag] = []
+  contents.split(', ').map do |content|
+    match = /^(\d+) ([\w\s]+) bags?\.?$/.match(content.strip)
+    if match
+      number = match[1].to_i
+      color = match[2]
+      rules[bag].push [color, number]
+    else
+      contains[bag] = 0
+    end
+  end
+end
+
+changed = true
+while changed
+  changed = false
+  rules.each do |bag, productions|
+    if !contains[bag]
+      if productions.all? { |rule| contains[rule[0]] }
+        contains[bag] = productions.reduce(0) do |bags, rule|
+          bags + (1 + contains[rule[0]]) * rule[1]
+        end
+        changed = true
+        rules.delete bag
+      end
+    end
+  end
+end
+
+puts contains['shiny gold']
-- 
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