diff --git a/2016/ruby/day_13.rb b/2016/ruby/day_13.rb
index 7613cfe..da3beb6 100644
--- a/2016/ruby/day_13.rb
+++ b/2016/ruby/day_13.rb
@@ -2,23 +2,55 @@ class Maze
   attr_reader :walls
 
   def initialize(seed)
-    @walls = Hash.new {|h,k|
-      x,y = k
+    @walls = Hash.new {|h,(x,y)|
       num = x*x + 3*x + 2*x*y + y + y*y + seed
-      h[k] = num.to_s(2).chars.count {|c| c == ?1 }.odd?
+      h[[x,y]] = num.to_s(2).chars.count {|c| c == ?1 }.odd?
     }
   end
 
   def [](x,y)
     walls[[x, y]]
   end
+
+  def solve(from, to)
+    seen = Set.new
+    current = [[from, 0]]
+    loop do
+      pos, count = current.shift
+      seen << pos
+      x,y = pos
+
+      [[1,0], [-1,0], [0,1], [0,-1]].map {|dx, dy|
+        [x + dx, y + dy]
+      }.reject {|x,y|
+        x.negative? || y.negative?
+      }.reject {|x,y|
+        walls[[x,y]]
+      }.reject {|x,y|
+        seen.include?([x,y])
+      }.each do |x,y|
+        return count + 1 if to == [x,y]
+
+        current << [[x,y], count + 1]
+      end
+    end
+  end
 end
 
-require 'minitest/autorun'
+if __FILE__ == $0
+  maze = Maze.new(1358)
+  puts maze.solve([1,1], [31,39])
+end
+
+require 'minitest'
+# require 'minitest/autorun'
 
 class TestMaze < Minitest::Test
+  def setup
+    @maze = Maze.new(10)
+  end
+
   def test_maze
-    maze = Maze.new(10)
     maze_s = <<-MAZE.chomp.split("\n").map(&:chars)
 .#.####.##
 ..#..#...#
@@ -30,8 +62,12 @@ class TestMaze < Minitest::Test
     MAZE
     maze_s.each.with_index do |row, y|
       row.each.with_index do |c, x|
-        assert_equal c, maze[x,y] ??#:?.
+        assert_equal c, @maze[x,y] ??#:?.
       end
     end
   end
+
+  def test_solve
+    assert_equal 11, @maze.solve([1,1], [7,4])
+  end
 end