gistfile1.txt

        /**
         * Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
         */
        public void addAtHead(int val)
        {
            Link link = new Link(val);
            //-->
            head.next.prev = link;
            link.next = head.next;
            //<--
            head.next = link;
            link.prev = head;
            size++;
        }