编写程序实现链式存储结构的循环队列，要求用带头结点 和尾指针的循环链表实现，编写函数分别完成队列初始化、入队、出 队、输出队列数据、队列置空、判断队列是否为空的功能。

在Python中，我们可以使用类来实现循环队列，使用一个头节点（front）和尾节点（rear）来指示链表的起始位置。以下是关键部分的实现：

class Node:
    def __init__(self, data=None):
        self.data = data
        self.next = None

class CircularQueue:
    def __init__(self, capacity):
        self.capacity = capacity
        self.front = self.rear = -1
        self.queue = [None] * capacity

    # 初始化队列
    def enqueue(self, data):
        if (self.rear + 1) % self.capacity == self.front:
            print("Queue is full.")
        else:
            if self.front == -1:
                self.front = self.rear = 0
            new_node = Node(data)
            self.queue[self.rear] = new_node
            self.rear = (self.rear + 1) % self.capacity

    # 出队操作
    def dequeue(self):
        if self.is_empty():
            print("Queue is empty.")
        else:
            removed_data = self.queue[self.front]
            next_node = self.queue[(self.front + 1) % self.capacity]
            self.queue[self.front] = None
            if self.front == self.rear:
                self.front = self.rear = -1
            else:
                self.front = (self.front + 1) % self.capacity
            return removed_data

    # 检查队列是否为空
    def is_empty(self):
        return self.front == -1 and self.rear == -1

    # 输出队列数据
    def display(self):
        if self.is_empty():
            print("Queue is empty.")
        else:
            current = self.front
            while True:
                print(self.queue[current], end=" ")
                current = (current + 1) % self.capacity
                if current == self.front:
                    break
            print()

    # 清空队列
    def queue_clear(self):
        self.front = self.rear = -1
        for node in self.queue:
            node = None


# 示例
cq = CircularQueue(5)
cq.enqueue(1)
cq.enqueue(2)
cq.enqueue(3)
cq.display()  # 输出：1 2 3 (empty spaces)

cq.dequeue()
cq.display()  # 输出：2 3 (empty spaces)

print(cq.is_empty())  # 输出：False
cq.queue_clear()
print(cq.is_empty())