code: @Nonnull
    @Override
    public Seq<E> distinct() {
      final HashSet<E> elements = new HashSet<>();
      final SeqBuilder<E> builder = Seq.builder(size());
      forEach(element -> {
        if (!elements.contains(element)) {
          builder.add(element);
          elements.add(element);
        }
      });
      return builder.result();
    }
docs: Returns a copy of this Seq with no duplicates.
  <p>
  Order is maintained.