题解 | #用两个栈实现队列#

class Solution:
    def __init__(self):
        self.stack1 = []
        self.stack2 = []
    def push(self, node):
        # write code here
        self.stack1.append(node)
    def pop(self):
        # return xx
        if self.stack2 == []:
            while self.stack1 != []:
                self.stack2.append(self.stack1.pop())
        return self.stack2.pop()

注意：None与空列表[]是不一样的！