diff --git a/2018/ruby/day_02.rb b/2018/ruby/day_02.rb
new file mode 100644
index 0000000..df0945a
--- /dev/null
+++ b/2018/ruby/day_02.rb
@@ -0,0 +1,11 @@
+a = ARGF.read.lines.map(&:chomp).map(&:chars)
+# two = a.count {|i| i.any? {|x| i.count(x) == 2} }
+# three = a.count {|i| i.any? {|x| i.count(x) == 3} }
+# puts two * three
+x,y = a.flat_map {|i|
+  a.select {|j|
+    i.zip(j).select {|a,b| a != b }.count == 1
+  }
+}.map(&:join)
+
+p x.chars.zip(y.chars).select {|a,b| a == b }.map(&:first).join