diff --git a/2018/ruby/day_04.rb b/2018/ruby/day_04.rb
new file mode 100644
index 0000000..2d32a81
--- /dev/null
+++ b/2018/ruby/day_04.rb
@@ -0,0 +1,23 @@
+records = ARGF.read.chomp.lines.map(&:chomp).sort
+# puts records
+
+stats = Hash.new {|h,k| h[k] = [] }
+
+guard = nil
+fell_asleep_at = nil
+records.each do |record|
+  if record =~ /\[\d{4}-\d{2}-\d{2} \d{2}:\d{2}\] Guard \#(\d+) begins shift/
+    guard = $1.to_i
+  elsif record =~ /\[\d{4}-\d{2}-\d{2} \d{2}:(\d{2})\] falls asleep/
+    fell_asleep_at = $1.to_i
+  elsif record =~ /\[\d{4}-\d{2}-\d{2} \d{2}:(\d{2})\] wakes up/
+    stats[guard] << (fell_asleep_at...$1.to_i)
+  else
+    p record
+  end
+end
+
+guard, (minute, _) = stats.map {|k,v|
+  [k, v.flat_map(&:to_a).group_by {|x| x }.max_by {|_,v| v.count }]
+}.max_by {|_,(_,v)| v.count }
+p guard * minute