环形队列的各种基本运算

以下是环形队列的各种基本运算：

1.初始化队列

def __init__(self, maxsize=None):
    self.maxsize = maxsize
    self._items = [None] * maxsize
    self.front = 0
    self.rear = 0
    self.tag = 0

2.判断队列是否为空

def is_empty(self):
    return self.front == self.rear and not self.tag

3.判断队列是否已满

def is_full(self):
    return self.front == self.rear and self.tag

4.入队操作

def enqueue(self, item):
    if self.is_full():
        raise Exception('Queue is full')
    self._items[self.rear] = item
    self.rear = (self.rear + 1) % self.maxsize
    self.tag = 1

5.出队操作

def dequeue(self):
    if self.is_empty():
        raise Exception('Queue is empty')
    item = self._items[self.front]
    self.front = (self.front + 1) % self.maxsize
    self.tag = 0
    return item