剑指05-用两个栈实现队列

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题目描述

用两个栈来实现一个队列，完成队列的Push和Pop操作。 队列中的元素为int类型。

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class MyStack:
    def __init__(self):
        self.stack = []
    def push(self, x):
        self.stack.append(x)
    def pop(self):
        if len(self.stack) == 0:
            return None
        val = self.stack[-1]
        self.stack = self.stack[:-1]
        return val
    def length(self):
        return len(self.stack)

class Solution:
    def __init__(self):
        self.stack1 = MyStack()
        self.stack2 = MyStack()
    def push(self, node):
        # write code here
        self.stack1.push(node)
    def pop(self):
        # return xx
        while self.stack1.length() > 0:
            self.stack2.push(self.stack1.pop())
        val = self.stack2.pop()
        while self.stack2.length() > 0:
            self.stack1.push(self.stack2.pop())
        return val