diff --git a/2018/ruby/day_09.rb b/2018/ruby/day_09.rb
new file mode 100644
index 0000000..64f4068
--- /dev/null
+++ b/2018/ruby/day_09.rb
@@ -0,0 +1,35 @@
+ARGF.read.chomp =~ /(\d+) players; last marble is worth (\d+) points/
+num_players = $1.to_i
+num_marbles = $2.to_i
+
+circle = []
+marbles = (0...num_marbles).to_a
+
+zero = marbles.shift
+circle << zero
+
+current_marble_index = 0
+current_player = 0
+scores = Hash.new(0)
+
+until marbles.empty?
+  current_marble = marbles.shift
+
+  if current_marble % 23 == 0
+    scores[current_player] += current_marble
+    index = (current_marble_index - 7) % circle.size
+    scores[current_player] += circle.delete_at(index)
+    current_marble_index = index
+  else
+    index = (current_marble_index + 2) % circle.size - 1
+    index += 1 unless index == -1
+    circle.insert(index, current_marble)
+    current_marble_index = index % circle.size
+  end
+
+  # puts "[#{current_player + 1}] #{circle.join(" ")}"
+
+  current_player = (current_player + 1) % num_players
+end
+
+p scores.max_by(&:last)