Blogger - Folding tree - 1

sealed trait Tree[E]
case class Empty[E]() extends Tree[E]
case class Node[E](el: E, left: Tree[E], right: Tree[E]) extends Tree[E]

def toListSimple[A](tree: Tree[A]): List[A] = tree match {
  case Node(el, left, right) => toListSimple(left) ::: (el :: toListSimple(right))
  case Empty() => Nil
}

def toList[A](tree: Tree[A]): List[A] = {
  def toListBuffer(tree: Tree[A], b: ListBuffer[A]): ListBuffer[A] = tree match {
    case Node(el, left, right) => {
      toListBuffer(left, b)
      b += el
      toListBuffer(right, b)
    }
    case Empty() => b
  }
  toListBuffer(tree, new ListBuffer[A]).toList
}