堆

# queue，先进先出(FIFO: First In First Out)


class Queue(object):
    """堆"""

    def __init__(self):
        """创建一个空的队列"""
        self.data = []

    def enqueue(self, item):
        """往队列中添加一个item元素"""
        self.data.append(item)

    def dequeue(self):
        """从队列头部删除一个元素"""
        return self.data.pop(0)

    def is_empty(self):
        """判断一个队列是否为空"""
        return self.data == []

    def size(self):
        """返回队列的大小"""
        return len(self.data)


if __name__ == '__main__':
    queue = Queue()
    print(queue.is_empty())
    queue.enqueue(1)
    queue.enqueue(3)
    queue.enqueue(2)
    print(queue.is_empty())
    print(queue.dequeue())
    print(queue.dequeue())
    print(queue.dequeue())