BinaryNode(int x, Optional<BinaryNode> left, Optional<BinaryNode> right) {
      this.x = x;
      this.left = left;
      this.right = right;
    }
  }

  enum Topology {
    BALANCED {
      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {
        if (size == 0) {
          return Optional.absent();
        } else {
          int leftChildSize = (size - 1) / 2;

    BinaryNode(int x, Optional<BinaryNode> left, Optional<BinaryNode> right) {
      this.x = x;
      this.left = left;
      this.right = right;
    }
  }

  enum Topology {
    BALANCED {
      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {
        if (size == 0) {
          return Optional.absent();
        } else {
          int leftChildSize = (size - 1) / 2;

   * if {@code n == 0}.
   *
   * <p><b>Warning:</b> the result takes <i>O(n log n)</i> space, so use cautiously.
   *
   * <p>This uses an efficient binary recursive algorithm to compute the factorial with balanced
   * multiplies. It also removes all the 2s from the intermediate products (shifting them back in at
   * the end).
   *
   * @throws IllegalArgumentException if {@code n < 0}
   */

 *           // Services have been initialized and are healthy, start accepting requests...
 *         }
 *         public void failure(Service service) {
 *           // Something failed, at this point we could log it, notify a load balancer, or take
 *           // some other action.  For now we will just exit.
 *           System.exit(1);
 *         }
 *       },
 *       MoreExecutors.directExecutor());
 *