scala implementing binary tree end nodes using Option

Question

I am trying to implement end nodes in my Binary Tree. I am wondering why this doesnt work:

// I thought that by adding Option, I can enter None as an allowed Node[T]. But neither p1 or p2 allows me to compile. How can I make this work?

class Node[T](text: String, one: Option[Node[T]], two: Node[T]) {
  override def toString = "(" + one + ", " + two + ")"
}

object GenTest {
  def main(args: Array[String]) {
    val p1 = new Node("wait", "test", "test")
    val p2 = new Node("odd", p1, p1)

    println(p1)
  }
}

Lee · Accepted Answer · 2014-11-27 20:15:29Z

1

"test" is not an Option[Node[String]]]. You need to create a leaf node and then pass it to the parent using Some:

class Node[T](text: String, one: Option[Node[T]], two: Option[Node[T]]) {
  override def toString = "(" + one + ", " + two + ")"
}

val leaf = new Node[String]("test", None, None)
val p1 = new Node("wait", Some(leaf), Some(leaf))
val p2 = new Node("wait", Some(p1), Some(p1))

edited Nov 27, 2014 at 20:15

answered Nov 27, 2014 at 20:03

Lee

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5 Comments

user1639926 Over a year ago

hey, can you explain that to me? Also this doesn't work. It refuses to compile saying: found : Some[Node[Nothing]] required: Option[Node[T]]

Lee Over a year ago

@user1639926 - You need to change the type of two to be Option[Node[T]] as well, see update.

user1639926 Over a year ago

i did, the error is occuring p1: Error:(12, 51) type mismatch; found : Some[Node[Nothing]] required: Option[Node[T]] val p1 = new Node("wait", Some(leaf), Some(leaf)) ^

Lee Over a year ago

@user1639926 - Sorry, you also need to supply the type of T when creating leaf, updated.

user1639926 Over a year ago

why do you need to supply type T in leave but not in p1 or p2?

grzenio · Accepted Answer · 2014-11-27 20:10:40Z

0

First of all parameter two should also be Option[Node[T]].
Second: You need to use option if you declared it:

class Node[T](text: String, one: Option[Node[T]], two: Option[Node[T]]) {
  override def toString = text + " (" + one + ", " + two + ")"
}

object GenTest {
  def main(args: Array[String]) {
    val p1 = new Node[String]("wait", None, None)
    val p2 = new Node("odd", Some(p1), Some(p1))

    println(p1)
  }
}

answered Nov 27, 2014 at 20:10

grzenio

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