code: public static <T> TopKSelector<T> least(int k, Comparator<? super T> comparator) {
      return new TopKSelector<T>(comparator, k);
    }
docs: Returns a {@code TopKSelector} that collects the lowest {@code k} elements added to it,
  relative to the specified comparator, and returns them via {@link #topK} in ascending order.
  
  @throws IllegalArgumentException if {@code k < 0}