2.1 Dedup linkedlist

Write code to remove duplicates from an unsorted linked list

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trait Node {
  def value: Int
  def next: Node
}

object Empty extends Node {
  def value: Int = throw new Error("access empty variable")
  def next: Node = throw new Error("access empty variable")
}

case class NonEmpty(value: Int, next: Node = null) extends Node

def toLinkedList(lst: List[Int]): Node = {
  if (lst.isEmpty) Empty
  else new NonEmpty(lst.head, toLinkedList(lst.tail))
}

def printLinkedList(head: Node): Unit = head match {
  case Empty =>
  case node: NonEmpty => {
    println(node.value)
    printLinkedList(node.next)
  }
}

/**
  * 2.1
  *
  * @param head
  * @return
  */
def deduplicate(head: Node): Node = {
  val dict = scala.collection.mutable.Map[Int, Boolean]()
  def dedup(node: Node): Node = {
    node match {
      case Empty => Empty
      case current: NonEmpty => {
        dict.get(current.value) match {
          case Some(value) => dedup(current.next)
          case None => {
            dict += (current.value -> true)
            new NonEmpty(current.value, dedup(current.next))
          }
        }
      }
    }
  }
  dedup(head)
}

var node = toLinkedList(List(1, 2, 3, 4, 4, 5, 6, 6))
printLinkedList(deduplicate(node))