--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/distances.rb	Sun Sep 15 11:46:47 2019 +0200
@@ -0,0 +1,60 @@
+#---
+# Excerpted from "Mazes for Programmers",
+# published by The Pragmatic Bookshelf.
+# Copyrights apply to this code. It may not be used to create training material, 
+# courses, books, articles, and the like. Contact us if you are in doubt.
+# We make no guarantees that this code is fit for any purpose. 
+# Visit http://www.pragmaticprogrammer.com/titles/jbmaze for more book information.
+#---
+class Distances
+  def initialize(root)
+    @root = root
+    @cells = {}
+    @cells[@root] = 0
+  end
+
+  def [](cell)
+    @cells[cell]
+  end
+
+  def []=(cell, distance)
+    @cells[cell] = distance
+  end
+
+  def cells
+    @cells.keys
+  end
+
+  def path_to(goal)
+    current = goal 
+
+    breadcrumbs = Distances.new(@root) 
+    breadcrumbs[current] = @cells[current]
+
+    until current == @root 
+      current.links.each do |neighbor| 
+        if @cells[neighbor] < @cells[current] 
+          breadcrumbs[neighbor] = @cells[neighbor] 
+          current = neighbor
+          break
+        end
+      end
+    end
+
+    breadcrumbs
+  end
+
+  def max
+    max_distance = 0
+    max_cell = @root
+
+    @cells.each do |cell, distance|
+      if distance > max_distance
+        max_cell = cell
+        max_distance = distance
+      end
+    end
+
+    [max_cell, max_distance]
+  end
+end