diff --git a/2023/ruby/day_12.rb b/2023/ruby/day_12.rb
new file mode 100644
index 0000000..97cfc1d
--- /dev/null
+++ b/2023/ruby/day_12.rb
@@ -0,0 +1,14 @@
+p ARGF.readlines(chomp: true).map {|row|
+  springs, groups = row.split(" ")
+  [springs, groups.scan(/\d+/).map(&:to_i)]
+}.map {|springs, groups|
+  unknowns = springs.count(??)
+  (0...2**unknowns).map {|arrangement|
+    arrangement = arrangement.to_s(2).rjust(unknowns, ?0).chars.map { _1 == ?0 ? ?. : ?# }
+    candidate = springs.gsub(??) { arrangement.shift }
+    candidate.chars
+      .slice_when { _1 != _2 }
+      .reject { _1[0] == ?. }
+      .map(&:size) == groups
+  }.count(&:itself)
+}.sum