code: public static <T> void resetVertices(List<Vertex<T>> vertices)
      {
          Iterator<Vertex<T>> it = vertices.iterator();
          while (it.hasNext())
          {
              it.next().reset();
          }
      }
docs: Resets all the vertices so that the visitation flags and indegrees are
  reset to their start values.
  
  @param vertices