Implement a MyQueue class which implements a queue using two stacks.

QueueViaStacks.scala

/**
  * Implement a MyQueue class which implements a queue using two stacks.
  * Time Complexity
  * Enqueue O(1), DeQueue O(n) if dequeue called after each enqueue
  * Space complexity O(n)
  * Created by Arun Sethia on 7/30/18.
  */
case class QueueViaStacks(stack: List[Int], queue: List[Int] = Nil) {

  def enQueue(elem: Int) = QueueViaStacks(elem :: stack, queue)

  def deQueue() = {
    queue match {
      case Nil if (!stack.isEmpty) => {
        val newQueue = stack.foldLeft(List.empty[Int])((a, b) => b :: a)
        println(s"dequeue :${newQueue.head}")
        QueueViaStacks(Nil, newQueue.tail)
      }
      case Nil if (stack.isEmpty) => {
        throw new UnsupportedOperationException("queue is empty")
      }
      case h :: _ => {
        println(s"dequeue ${h}")
        QueueViaStacks(stack, queue.tail)
      }
    }
  }
}