题目

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

解题思路

class CQueue:
    def __init__(self):
        self.queueListOut = []
        self.queueListTemp = []
    def appendTail(self, value: int) -> None:
        self.queueListTemp.append(value)

    def deleteHead(self) -> int:
        if len(self.queueListOut) <= 0 and len(self.queueListTemp)<= 0: return -1
        if len(self.queueListOut) != 0:
            return self.queueListOut.pop()
        while len(self.queueListTemp) != 0:
            self.queueListOut.append(self.queueListTemp.pop())
        return self.queueListOut.pop()