代码随想训练营第十天（Python）｜ 232.用栈实现队列 、 225. 用队列实现栈

232.用栈实现队列

class MyQueue:

    def __init__(self):
        self.stack_in = list()
        self.stack_out = list()


    def push(self, x: int) -> None:
        self.stack_in.append(x)


    def pop(self) -> int:
        if self.empty():
            return None
        if self.stack_out:
            return self.stack_out.pop()
        else:
            while self.stack_in:
                self.stack_out.append(self.stack_in.pop())
            return self.stack_out.pop()


    def peek(self) -> int:
        node = self.pop()
        if node:
            self.stack_out.append(node)
        return node


    def empty(self) -> bool:
        return not (self.stack_in or self.stack_out)

225. 用队列实现栈

class MyStack:

    def __init__(self):
        self.queue1 = list()
        self.queue2 = list()

    def push(self, x: int) -> None:
        self.queue1.append(x)


    def pop(self) -> int:
        if self.empty():
            return None
        if self.queue1:
            for i in range(len(self.queue1)-1):
                self.queue2.append(self.queue1.pop(0))
            res = self.queue1.pop(0)
            self.queue1, self.queue2 = self.queue2, self.queue1
            return res

    def top(self) -> int:
        res = self.pop()
        if res:
            self.push(res)
        return res


    def empty(self) -> bool:
        return not self.queue1