diff --git a/2024/ruby/day_09.rb b/2024/ruby/day_09.rb
new file mode 100644
index 0000000..a1053ad
--- /dev/null
+++ b/2024/ruby/day_09.rb
@@ -0,0 +1,21 @@
+disk_map = DATA.read.chars.each_slice(2)
+  .flat_map.with_index {|(a,b),i|
+    [ Array.new(a.to_i, i), Array.new(b.to_i, nil) ]
+  }.reject(&:empty?)
+
+while (prev, free = disk_map.each_cons(2).find { _2.include?(nil) })
+  tail = disk_map.last
+  until free.empty? || tail.empty?
+    prev << tail.shift
+    free.pop
+  end
+
+  while disk_map.last.all?(&:nil?)
+    disk_map.pop
+  end
+end
+
+pp disk_map.flatten.each.with_index.sum { _1 * _2 }
+
+__END__
+2333133121414131402