diff --git a/2022/ruby/day_13.rb b/2022/ruby/day_13.rb
new file mode 100644
index 0000000..21331c4
--- /dev/null
+++ b/2022/ruby/day_13.rb
@@ -0,0 +1,35 @@
+def compare(left, right)
+  case [left, right]
+  in [left, nil]
+    1
+  in [Integer, Integer]
+    left <=> right
+  in [Array, Array]
+    left.zip(right).each do |left, right|
+      case compare(left, right)
+      when -1 then return -1
+      when 0 # no-op
+      when 1 then return 1
+      end
+    end
+    (left.size == right.size) ? 0 : -1
+  else
+    compare(Array(left), Array(right))
+  end
+end
+
+# part one
+# pairs = ARGF.read.split("\n\n")
+# pairs = pairs.map {|pair| pair.lines(chomp: true).map { eval(_1) }}
+
+# p pairs.map.with_index {|(left,right),i|
+#   [compare(left, right), i+1]
+# }.select {|cmp,_| cmp == -1 }.sum(&:last)
+
+# part two
+pairs = ARGF.read.lines(chomp: true).reject(&:empty?).map { eval(_1) }
+pairs << [[2]] << [[6]]
+pairs = pairs.sort { compare(_1, _2) }
+a = pairs.index([[2]])
+b = pairs.index([[6]])
+p (a+1)*(b+1)