public void connect(TreeLinkNode root) {
        TreeLinkNode cur  = root;
        while(cur != null){
            TreeLinkNode head = new TreeLinkNode(-1); // 用于辅助编程，有辅助节点之后 代码精炼一些。
            TreeLinkNode pre = head;
            while(cur != null){
                if(cur.left != null){
                    pre.next = cur.left;
                    pre = pre.next;
                }
                if(cur.right != null){
                    pre.next = cur.right;
                    pre = pre.next;
                }
                cur = cur.next;
            }
            cur = head.next;
        }
    }