Best 2012 (b)

block.rb

    
valid_routes = add_segments(current_stops, starting_routes(start), stop) { |current, open_routes, matching_routes| current >= max_stops }


def add_segments(current_stops, routes, stop, matching_routes = [], &block )
  # This method expects a block that receives the parameters current_stops, open_routes and matching_routes
  # When the passed block evaluates to true
  # it returns all of the routes found matching the start and stop locations
  matching_routes << routes.select { |route| route.last_stop == stop }
  matching_routes.compress!
      
  open_routes = routes.select { |route| route.last_stop != stop }
  open_routes.compress!
      
  # Return all matches once we have satisfied our block 
  if open_routes && !open_routes.empty? && matching_routes && !matching_routes.empty?
    return matching_routes if yield current_stops, open_routes, matching_routes
  end
  
  # recursive call
  add_segments(current_stops + 1, next_routes(routes), stop, matching_routes, &block)
end

Again, I like this snippet of code because it represents a transition in my thinking as it is the first time I created real code that accepts a block as a parameter