假设以带头结点的循环链表表示队列，并且只设一个指针指向对尾结点，不设头指针，试设计相应的置队空、入队和出队的程序。-Assumed to take the lead in the circular linked list of nodes to the queue, and allowed only a pointer to the node-to-tail, no head pointer, try to design the home team empty, enqueue and dequeue procedure.