sealed trait BT[+A]

case object Empty extends BT[Nothing]

case class Node[+A](elem: A, left: BT[A], right: BT[A]) extends BT[A]

val t = Node(1, Node(2, Empty, Node(3, Empty, Empty)), Empty)

// Zadanie 1

def sumaBT[A](bt: BT[Int]): Int = bt match {
  case Node(elem, left, right) => elem + sumaBT(left) + sumaBT(right)
  case Empty => 0
}

sumaBT(t)

// Zadanie 2

def foldBT[A,B](f: A => (B,B) => B)(acc:B)(bt:BT[A]):B = bt match {
  case Node(value, l, r) => f(value)(foldBT(f)(acc)(l), foldBT(f)(acc)(r))
  case Empty => acc
}

def foldBT2[A,B](f: A => (B,B) => B)(acc:B)(bt:BT[A]):B = bt match {
  case Node(value, l, r) => foldBT2(f)(f(value)(foldBT(f)(acc)(l), foldBT(f)(acc)(r)))(bt)
  case Empty => acc
}