public static int getLenth(Node head){
        if (head.next == null) {
            return 0;
        }
        int lenth = 0;
        //让辅助指针指向头结点的下一个，就没有统计头结点
        Node temp = head.next;
        while(temp != null){
            temp = temp.next;
            lenth++;
        }
        return lenth;
    }