public IEnumerable <T> BackEnumerator()
        {
            DoublyNode <T> current = tail;

            while (current != null)
            {
                yield return(current.Data);

                current = current.Previous;
            }
        }
        public IEnumerator <T> GetEnumerator()
        {
            DoublyNode <T> current = head;

            while (current != null)
            {
                yield return(current.Data);

                current = current.Next;
            }
        }
        public bool Countains(T data)
        {
            DoublyNode <T> current = head;

            while (current != null)
            {
                if (current.Data.Equals(data))
                {
                    return(true);
                }
            }
            return(false);
        }
        public void Add(T data)
        {
            DoublyNode <T> node = new DoublyNode <T>(data);

            if (head == null)
            {
                head = node;
            }
            else
            {
                tail.Next     = node;
                node.Previous = tail;
            }
            tail = node;
            count++;
        }
        public void AddFirst(T data)
        {
            DoublyNode <T> node = new DoublyNode <T>(data);
            DoublyNode <T> temp = head;

            node.Next = temp;
            head      = node;
            if (count == 0)
            {
                tail = head;
            }
            else
            {
                temp.Previous = node;
            }
            count++;
        }
        public bool Remove(T data)
        {
            DoublyNode <T> current = head;

            while (current != null)
            {
                if (current.Data.Equals(data))
                {
                    break;
                }
                current = current.Next;
            }

            if (current != null)
            {
                if (current.Next != null)
                {
                    current.Next.Previous = current.Previous;
                }
                else
                {
                    tail = current.Previous;
                }

                if (current.Previous != null)
                {
                    current.Previous.Next = current.Next;
                }
                else
                {
                    head = current.Next;
                }
                count--;
                return(true);
            }
            return(false);
        }
 public void Clear()
 {
     head  = null;
     tail  = null;
     count = 0;
 }