diff --git a/2017/ruby/day_12.rb b/2017/ruby/day_12.rb
new file mode 100644
index 0000000..0470e02
--- /dev/null
+++ b/2017/ruby/day_12.rb
@@ -0,0 +1,19 @@
+require "set"
+h = Hash[ARGF.read.strip.scan(/(\d+) <-> ([\d, ]+)/).map {|a,b| [a.to_i, b.scan(/\d+/).map(&:to_i)]}]
+count = 0
+until h.empty?
+  key = h.keys.first
+  foo = Set.new
+  foo << key
+  bar = [key]
+  until bar.empty?
+    baz = bar.shift
+    bar = bar.concat(h[baz] - foo.to_a)
+    foo = foo.merge(h[baz])
+  end
+  count += 1
+  foo.each do |k|
+    h.delete(k)
+  end
+end
+p count