start multiple paths

21/main.rb

@@ -74,6 +74,14 @@ def dijkstra_with_lookup(graph, movements, start_char, target_char)
   dijkstra(graph, movements, start, target)
 end
 
+def dijkstra_paths(prev, target, current_path = [])
+  return [current_path.reverse] if prev[target].nil?
+
+  prev[target].flat_map do |parent|
+    dijkstra_paths(prev, parent, current_path + [target])
+  end
+end
+
 def dijkstra(graph, movements, start, target)
   queue = PriorityQueue.new
   dest = Hash.new
@@ -90,22 +98,20 @@ def dijkstra(graph, movements, start, target)
       .map { @arrow_dirs[_1] }
       .map { |dx, dy| [node.first + dx, node.last + dy] }
       .each do |neighbor|
-        if dest[neighbor].nil? || moves + 1 < dest[neighbor]
+        new_moves = moves + 1
-          dest[neighbor] = moves + 1
+        if dest[neighbor].nil? || new_moves < dest[neighbor]
-          prev[neighbor] = node
+          dest[neighbor] = new_moves
-          queue << [neighbor, moves + 1]
+          prev[neighbor] = [node]
+          queue << [neighbor, new_moves]
+        elsif new_moves == dest[neighbor]
+          prev[neighbor] << node
         end
       end
   end
 
-  path = Array.new
+  paths = dijkstra_paths(prev, target)
-  u = target
-  while prev[u]
-    path.unshift(u)
-    u = prev[u]
-  end
 
-  return dest, path
+  return dest, paths.first
 end
 
 # calculate most efficient number pad paths
@@ -145,6 +151,7 @@ robot_2 = input
   .map { _1.each_cons(2).to_a }
   .map { _1.map { |move| number_cache[move].join }.join("A") + "A" }
 
+debugger
 
 robot_3 = robot_2
   .map { _1.chars }