Linked list

class LinkedList<T> {

  private var head: Node<T>? = null
  private var tail: Node<T>? = null
  private var size = 0

  fun isEmpty(): Boolean {
    return size == 0
  }

  override fun toString(): String {
    if (isEmpty()) {
      return "Empty list"
    } else {
      return head.toString()
    }
  }

class Node<T>(val value: T) {
    var next: Node<T>? = null
}

class LinkedList<T> {
    private var head: Node<T>? = null

    fun push(value: T) {
        val node = Node(value)
        node.next = head
        head = node
    }

    fun pop(): T? {
        if (head == null) return null

        val value = head!!.value
        head = head!!.next

        return value
    }

    override fun toString(): String {
        var current = head
        var str = ""

        while (current != null) {
            str += "${current.value} -> "
            current = current.next
        }

        return str + "null"
    }

}