*/
  public static <N> boolean hasCycle(Graph<N> graph) {
    int numEdges = graph.edges().size();
    if (numEdges == 0) {
      return false; // An edge-free graph is acyclic by definition.
    }
    if (!graph.isDirected() && numEdges >= graph.nodes().size()) {
      return true; // Optimization for the undirected case: at least one cycle must exist.
    }

   */
  public static <N> boolean hasCycle(Graph<N> graph) {
    int numEdges = graph.edges().size();
    if (numEdges == 0) {
      return false; // An edge-free graph is acyclic by definition.
    }
    if (!graph.isDirected() && numEdges >= graph.nodes().size()) {
      return true; // Optimization for the undirected case: at least one cycle must exist.
    }

      while (graph.edges().size() < NUM_EDGES) {
        graph.putEdge(getRandomElement(nodeList, gen), getRandomElement(nodeList, gen));
      }
      ArrayList<EndpointPair<Integer>> edgeList = new ArrayList<>(graph.edges());

      assertThat(graph.nodes()).hasSize(NUM_NODES);
      assertThat(graph.edges()).hasSize(NUM_EDGES);
      AbstractGraphTest.validateGraph(graph);

      assertThat(network.nodes()).hasSize(NUM_NODES);
      assertThat(network.edges()).hasSize(NUM_EDGES);
      AbstractNetworkTest.validateNetwork(network);

      Collections.shuffle(edgeList, gen);
      int numEdgesToRemove = gen.nextInt(NUM_EDGES);
      for (int i = 0; i < numEdgesToRemove; ++i) {
        Object edge = edgeList.get(i);
        assertThat(network.removeEdge(edge)).isTrue();

      while (graph.edges().size() < NUM_EDGES) {
        graph.putEdge(getRandomElement(nodeList, gen), getRandomElement(nodeList, gen));
      }
      ArrayList<EndpointPair<Integer>> edgeList = new ArrayList<>(graph.edges());

      assertThat(graph.nodes()).hasSize(NUM_NODES);
      assertThat(graph.edges()).hasSize(NUM_EDGES);
      AbstractGraphTest.validateGraph(graph);