public void convert(Node head){
        if(head == null){
            return;
        }
        
        Queue<Node> queue = new LinkedList<>();
        queue.add(head);
        head = head.next;
        while(head != null){
            Node top = queue.poll();
            top.before = head;
            head = head.next;
            if(head != null){
                top.next = head;
                head = head.next;
                //null the next of child before putting them into queue
                top.before.next = null;
                top.next.next = null;
                queue.add(top.before);
                queue.add(top.next);
            }else{
                break;
            }
        }
     }
http://www.geeksforgeeks.org/given-linked-list-representation-of-complete-tree-convert-it-to-linked-representation/
Test cases
Zero, One or more nodes in link list
src/com/interview/linklist/LinkListToCompleteBinaryTree.java