code: private void createVertexNumber()
      {
      	c = graph.vertexSet().size();
          vertexToVertexNumber = new HashMap<>(c);
  
          for (V vertex : graph.vertexSet()) {
              vertexToVertexNumber.put(vertex, new VertexNumber<V>(vertex, 0));            
          }
          
          stack = new ArrayDeque<>(c);
          B = new ArrayDeque<>(c);
      }
docs: /*
  Creates a VertexNumber object for every vertex in the graph and stores
  them in a HashMap.