Balanced Binary Tree

Implement a function to check if a binary tree i balanced. For the purposes of this question, a balanced tree is defined to be a tree such that the heights of the two subtrees of any node never differ by more than one

Scala

import scala.collection.mutable

trait BTree

object Empty extends BTree

case class Node(var value: Int, var left: BTree = Empty, var right: BTree = Empty) extends BTree

def printBTree(root: BTree): Unit = {
  val queue = mutable.Queue[(BTree, Int)]((root, 0))
  var prev = -1
  while (!queue.isEmpty) {
    val (node, level) = queue.dequeue()
    node match {
      case n: Node => {
        if (level != prev) {
          print("\n#")
          prev = level
        }
        print(n.value)
        queue.enqueue((n.left, level + 1))
        queue.enqueue((n.right, level + 1))
      }
      case _ =>
    }
  }
}

/**
  * 4.1
  *
  * @param root
  * @return
  */
def isBalanced(root: BTree): Boolean = {
  def depth(node: BTree): Int = {
    node match {
      case Empty => 0
      case n: Node => {
        val (left, right) = (depth(n.left), depth(n.right))
        if (left == -1 || right == -1 || math.abs(left - right) > 1) -1
        else (left max right) + 1
      }
    }
  }
  depth(root) != -1
}

val a = Node(1, Empty, Empty)
val b = Node(2, Empty, Empty)
val c = Node(3, a, b)

isBalanced(Empty)
isBalanced(c)

val e = Node(4, Empty, a)
val d = Node(5, Empty, e)
val f = Node(5, Empty, d)

isBalanced(f)

Second Tab