09_QueueWithTwoStacks.py

# -*- coding: utf-8 -*-
# @File    : 09_QueueWithTwoStacks.py
# @Date    : 2020-04-02
# @Author  : tc
"""
面试题09.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"]
[[],[3],[],[]]
输出：[null,null,3,-1]
示例 2：

输入：
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出：[null,-1,null,null,5,2]
提示：

1 <= values <= 10000
最多会对 appendTail、deleteHead 进行 10000 次调用

参考：https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof/solution/mian-shi-ti-09-yong-liang-ge-zhan-shi-xian-dui-l-2/

"""
class CQueue:

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

    def appendTail(self, value: int) -> None:
        self.stack1.append(value)

    def deleteHead(self) -> int:
        if self.stack2:
            return self.stack2.pop()
        if not self.stack1: return -1
        while self.stack1:
            self.stack2.append(self.stack1.pop())
        return self.stack2.pop()