private void PrintL(DListNode Node)
 {
     while (Node != null)
     {
         Console.Write("{0} ", Node.n);
         Node = Node.next;
     }
     Console.WriteLine();
 }
 public DListNode Insert(int n)
 {
     if (head == null && tail == null)
     {
         head = new DListNode(n);
         tail = head;
         return(head);
     }
     else
     {
         DListNode temp = new DListNode(n);
         tail.next = temp;
         temp.prev = tail;
         tail      = tail.next;
         return(tail);
     }
 }
 public DoubleLinkedList()
 {
     head = null;
     tail = null;
 }
 public DListNode(int n)
 {
     this.n = n;
     prev   = null;
     next   = null;
 }