佇列的儲存結構中使用的最多的是迴圈佇列。迴圈佇列包括兩個指標， front 指標指向隊頭元素， rear 指標指向隊尾元素的下一個位置。 佇列為空的判斷條件是：       front == rear 佇列滿的判斷條件是       (rear+1)%maxsize == front 佇列長度的計算公式：       (rear-front+maxsize)%maxsize

      正常情況下當front == rear是佇列有可能是滿也有可能是空，為了區分這兩種情況 我們需要在front前新增一個閒置單元。

示例

class MyCircularQueue:
    def
 
 __init__(self, k):
        """
        Initialize your data structure here. Set the size of the queue to be k.
        :type k: int
        """
        self.queue = [None] * (k + 1)
        self.maxsize = (k + 1)
        self.front = 0
        self.rear = 0

    def enQueue(self, value):
        """
        Insert an element into the circular queue. Return true if the operation is successful.
        :type value: int
        :rtype: bool
        """
 

        if self.isFull():
            return False
        self.queue[self.rear] = value
        self.rear = (self.rear + 1) % self.maxsize
        return True



    def deQueue(self):
        """
        Delete an element from the circular queue. Return true if the operation is successful.
        :rtype: bool
        """
 

        if self.isEmpty():
            return False
        self.queue[self.front] = None
        self.front = (self.front + 1) % self.maxsize
        return True

    def Front(self):
        """
        Get the front item from the queue.
        :rtype: int
        """
        if self.isEmpty():
            return -1
        return self.front

    def Rear(self):
        """
        Get the last item from the queue.
        :rtype: int
        """
        if self.isEmpty():
            return -1
        return self.rear

    def isEmpty(self):
        """
        Checks whether the circular queue is empty or not.
        :rtype: bool
        """
        return self.front == self.rear

    def isFull(self):
        """
        Checks whether the circular queue is full or not.
        :rtype: bool
        """
        return (self.rear + 1) % self.maxsize == self.front