剑指 Offer 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

Python 解答：

1.直白但是麻烦

class CQueue:

    def __init__(self):
        self.left = []
        self.right = []

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

    def deleteHead(self) -> int:
        if not self.left:
            return -1
        while self.left:
            temp = self.left.pop()
            self.right.append(temp)
        res = self.right.pop()
        while self.right:
            temp = self.right.pop()
            self.left.append(temp)
        return res

# Your CQueue object will be instantiated and called as such:
# obj = CQueue()
# obj.appendTail(value)
# param_2 = obj.deleteHead()

2.改进了一点

class CQueue:

    def __init__(self):
        self.left = []
        self.right = []

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

    def deleteHead(self) -> int:
        if not self.right:
            while self.left:
                temp = self.left.pop()
                self.right.append(temp)
        if self.right:
            return self.right.pop()
        else:
            return -1

# Your CQueue object will be instantiated and called as such:
# obj = CQueue()
# obj.appendTail(value)
# param_2 = obj.deleteHead()