diff --git a/2016/ruby/day_17.rb b/2016/ruby/day_17.rb
new file mode 100644
index 0000000..bfb6b38
--- /dev/null
+++ b/2016/ruby/day_17.rb
@@ -0,0 +1,44 @@
+require 'digest/md5'
+
+State = Struct.new(:location, :path)
+
+Maze = Struct.new(:passcode, :size) do
+  def walk
+    return enum_for(__method__) unless block_given?
+
+    states = [State.new([0,0], '')]
+    until states.empty?
+      state = states.shift
+      yield state
+
+      hash = Digest::MD5.hexdigest("#{passcode}#{state.path}")[0,4]
+      open_doors = %i[ U D L R ].select.with_index {|_, index|
+        'bcdef'.include?(hash[index])
+      }
+
+      {
+        U: [ 0, -1],
+        D: [ 0,  1],
+        L: [-1,  0],
+        R: [ 1,  0],
+      }.select {|door, _|
+        open_doors.include?(door)
+      }.map {|door, (dx, dy)|
+        x = state.location[0] + dx
+        y = state.location[1] + dy
+
+        location = [x, y]
+        path = state.path + door.to_s
+        State.new(location, path)
+      }.select {|state|
+        state.location.all? {|i| (0...size).cover?(i) }
+      }.each do |state|
+        states << state
+      end
+    end
+  end
+end
+
+p Maze.new('yjjvjgan', 4).walk.find {|state|
+  state.location == [3, 3]
+}