数据结构习题代码：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队尾元素结点而不设头指针，试编写相应的队列初始化、入队列、出队列和判断队列状态的算法。-Assuming lead to circular list node represents a queue, and only set up a pointer to the tail element nodes instead of being the head pointer, try to prepare the correspo