微信图片_20191219182351.jpg
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.stack1 == [] and self.stack2 == []:
return None
if self.stack2 == []:
while self.stack1:
self.stack2.append(self.stack1.pop())
return self.stack2.pop()
