232. Implement Queue using Stacks

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class Stack:
    def __init__(self):
        self.top = None

    def push(self, data):
        if self.top is None:
            self.top = Node(data)
        else:
            node = Node(data)
            node.next = self.top
            self.top = node

    def pop(self):
        if self.top is None:
            return None
        node = self.top
        self.top = self.top.next
        return node.data

    def peek(self):
        if self.top is None:
            return None
        return self.top.data

    def is_empty(self):
        return self.top is None

class MyQueue:
    def __init__(self):
        self.mystack = Stack()

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

    def pop(self) -> int:
        if self.mystack.top.next is None: return self.mystack.pop()
        node = self.mystack.top
        prev = None
        while node.next:
            prev = node
            node = node.next
        res = node.data
        prev.next = None
        return res


    def peek(self) -> int:
        node = self.mystack.top
        prev = None
        while node:
            prev = node
            node = node.next
        return prev.data

    def empty(self) -> bool:
        return self.mystack.is_empty()