def remove1b[A](xs: List[A])(p: A => Boolean): List[A] = {
  def removeTail[A](xs: List[A], acc: List[A])(p: A => Boolean): List[A] =
    xs match {
      case h :: t => if (p(h)) removeTail(Nil, acc:::t)(p) else removeTail(t, h::acc)(p)
      case _ => acc
    }

  removeTail(xs, Nil)(p)
}