}
      }
    } else {
      // An optimization for the undirected case: for every node B reachable from node A,
      // node A and node B have the same reachability set.
      Set<N> visitedNodes = new HashSet<>();
      for (N node : graph.nodes()) {
        if (!visitedNodes.contains(node)) {
          Set<N> reachableNodes = reachableNodes(graph, node);

    E duplicate = elements[(elements.length / 2) - 1];
    elements[(elements.length / 2) + 1] = duplicate;
    return new ArrayWithDuplicate<>(elements, duplicate);
  }

  // Helper methods to improve readability of derived classes

  protected int getNumElements() {
    return getSubjectGenerator().getCollectionSize().getNumElements();
  }

  protected Collection<E> getSampleElements(int howMany) {

    E duplicate = elements[(elements.length / 2) - 1];
    elements[(elements.length / 2) + 1] = duplicate;
    return new ArrayWithDuplicate<>(elements, duplicate);
  }

  // Helper methods to improve readability of derived classes

  protected int getNumElements() {
    return getSubjectGenerator().getCollectionSize().getNumElements();
  }

  protected Collection<E> getSampleElements(int howMany) {