*
   * @since 12.0
   */
  public static class Builder<E> extends ImmutableMultiset.Builder<E> {
    /*
     * We keep an array of elements and counts.  Periodically -- when we need more room in the
     * array, or when we're building, or the like -- we sort, deduplicate, and combine the counts.
     * Negative counts indicate a setCount operation with ~counts[i].
     */