/*
   * The subroutine of DFS. NOTE: the set is used to distinguish between 1st
   * and 2nd round of DFS. set == null: finished vertices are stored (1st
   * round). set != null: all vertices found will be saved in the set (2nd
   * round)
   */
  private void dfsVisit(
      DirectedGraph<V, E> visitedGraph, VertexData<V> vertexData, Set<V> vertices) {
    Deque<VertexData<V>> stack = new ArrayDeque<VertexData<V>>();
    stack.add(vertexData);

    while (!stack.isEmpty()) {
      VertexData<V> data = stack.removeLast();

      if (!data.isDiscovered()) {
        data.setDiscovered(true);

        if (vertices != null) {
          vertices.add(data.getVertex());
        }

        stack.add(new VertexData1<V>(data, true, true));

        // follow all edges
        for (E edge : visitedGraph.outgoingEdgesOf(data.getVertex())) {
          VertexData<V> targetData = vertexToVertexData.get(visitedGraph.getEdgeTarget(edge));

          if (!targetData.isDiscovered()) {
            // the "recursion"
            stack.add(targetData);
          }
        }
      } else if (data.isFinished()) {
        if (vertices == null) {
          orderedVertices.addFirst(data.getFinishedData());
        }
      }
    }
  }
 /** @see CrossComponentIterator.Specifics#edgesOf(Object) */
 public Set<? extends EE> edgesOf(VV vertex) {
   return graph.outgoingEdgesOf(vertex);
 }