用两个栈实现队列

#用两个栈实现队列

'''用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，
分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
示例 1：
输入：
["CQueue","appendTail","deleteHead","deleteHead","deleteHead"]
[[],[3],[],[],[]]
输出：[null,null,3,-1,-1]
示例 2：

输入：
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出：[null,-1,null,null,5,2]
'''
class CQueue(object):

    def __init__(self):
        self.stack1 = []
        self.stack2 = []

    def appendTail(self, value):
        """
        :type value: int
        :rtype: None
        """

        self.stack1.append(value)

    def deleteHead(self):
        """
        :rtype: int
        """
        if self.stack2 != []:
            return self.stack2.pop()

        if self.stack1 == []:
            return -1

        while self.stack1 != []:
            self.stack2.append(self.stack1.pop())
        return self.stack2.pop()