diff --git a/2016/ruby/day_18.rb b/2016/ruby/day_18.rb
new file mode 100644
index 0000000..9e13bcb
--- /dev/null
+++ b/2016/ruby/day_18.rb
@@ -0,0 +1,18 @@
+class Row
+  INPUT_MAP = { ?. => :safe, ?^ => :trap }
+
+  attr_reader :tiles
+
+  def initialize(input)
+    @tiles = input.chars.map {|char| INPUT_MAP.fetch(char) }
+  end
+end
+
+require 'minitest/autorun'
+
+class TestRow < Minitest::Test
+  def test_row
+    row = Row.new('..^^.')
+    assert_equal %i[ safe safe trap trap safe ], row.tiles
+  end
+end