* all "null" (UNSET).
   *
   * <p>A node with "prev" pointer equal to {@code ENDPOINT} is the first node in the linked list,
   * and a node with "next" pointer equal to {@code ENDPOINT} is the last node.
   */
  @CheckForNull @VisibleForTesting transient long[] links;

  /** Pointer to the first node in the linked list, or {@code ENDPOINT} if there are no entries. */
  private transient int firstEntry;

  /**
   * Pointer to the predecessor of an entry in insertion order. ENDPOINT indicates a node is the
   * first node in insertion order; all values at indices ≥ {@link #size()} are UNSET.
   */
  @CheckForNull private transient int[] predecessor;

  /**
   * Pointer to the successor of an entry in insertion order. ENDPOINT indicates a node is the last

/**
 * Indicates whether an endpoint of some range is contained in the range itself ("closed") or not
 * ("open"). If a range is unbounded on a side, it is neither open nor closed on that side; the
 * bound simply does not exist.
 *
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public enum BoundType {
  /** The endpoint value <i>is not</i> considered part of the set ("exclusive"). */

   */
  public abstract N target();

  /**
   * If this {@link EndpointPair} {@link #isOrdered()} returns the {@link #source()}; otherwise,
   * returns an arbitrary (but consistent) endpoint of the origin edge.
   */
  public final N nodeU() {
    return nodeU;
  }

  /**
   * Returns the node {@link #adjacentNode(Object) adjacent} to {@link #nodeU()} along the origin

/**
 * Indicates whether an endpoint of some range is contained in the range itself ("closed") or not
 * ("open"). If a range is unbounded on a side, it is neither open nor closed on that side; the
 * bound simply does not exist.
 *
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public enum BoundType {
  /** The endpoint value <i>is not</i> considered part of the set ("exclusive"). */

     * silently {@link #addNode(Object) add} each missing endpoint to the network.
     *
     * <p>If {@code edge} already connects an endpoint pair equal to {@code endpoints}, then this
     * method will have no effect.
     *
     * @return this {@code Builder} object
     * @throws IllegalArgumentException if {@code edge} already exists in the network and connects
     *     some other endpoint pair that is not equal to {@code endpoints}

     * <p>If this graph is directed, {@code endpoints} must be ordered.
     *
     * <p>If either or both endpoints are not already present in this graph, this method will
     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
     *
     * @return this {@code Builder} object
     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsSelfLoops()}

  /**
   * Pointer to the predecessor of an entry in insertion order. ENDPOINT indicates a node is the
   * first node in insertion order; all values at indices ≥ {@link #size()} are UNSET.
   */
  @CheckForNull private transient int[] predecessor;

  /**
   * Pointer to the successor of an entry in insertion order. ENDPOINT indicates a node is the last

   * visited twice if there is an edge connecting them. To avoid returning duplicate {@link
   * EndpointPair}s, we keep track of the nodes that we have visited. When processing endpoint
   * pairs, we skip if the "other node" is in the visited set, as shown below:
   *
   * <pre>
   * Nodes = {N1, N2, N3, N4}
   *    N2           __
   *   /  \         |  |
   * N1----N3      N4__|
   *

    firstEntry = ENDPOINT;
    lastEntry = ENDPOINT;
    links = new long[expectedSize];
    Arrays.fill(links, UNSET);
  }

  @Override
  int firstIndex() {
    return (firstEntry == ENDPOINT) ? -1 : firstEntry;
  }

  @Override
  int nextIndex(int index) {
    int result = getSuccessor(index);
    return (result == ENDPOINT) ? -1 : result;
  }

  @Override