# Implementation of the Queue ADT using a circular array.
from array import Array

class Queue:
    # Creates an empty queue
    def __init__(self, maxSize):
        self._count = 0
        self._front = 0
        self._back = maxSize - 1
        self._qArray = Array(maxSize)

    # Returns True if the queue is empty.
    def isEmpty(self):
        return self._count == 0

    # Retruns True if the queue is full.
    def isFull(self):
        return self._count == len(self._qArray)

    # Returns the number of items in the queue.
    def __len__(self):
        return self._count

    # Adds the given item to the queue.
    def enqueue(self, item):
        assert not self.isFull(), "Cannot enqueue to a full queue."
        maxSize = len(self._qArray)
        self._back = (self._back + 1) % maxSize
        self._qArray[self._back] = item
        self._count += 1

    # Removes and returns the first item in the queue.
    def dequeue(self):
        assert not self.isEmpty(), "Cannot dequeue from an empty queue."
        item = self._qArray[self._front]
        maxSize = len(self._qArray)
        self._front = (self._front + 1) % maxSize
        self._count -= 1
        return item