LeetCode--225--用队列实现栈

 1 class MyStack(object):
 2 
 3     def __init__(self):
 4         """
 5         Initialize your data structure here.
 6         """
 7         self.lists = []
 8 
 9     def push(self, x):
10         """
11         Push element x onto stack.
12         :type x: int
13         :rtype: void
14         """
15         self.lists.append(x)
16 
17     def pop(self):
18         """
19         Removes the element on top of the stack and returns that element.
20         :rtype: int
21         """
22         if len(self.lists) == 0:
23             return
24         return self.lists.pop()
25 
26     def top(self):
27         """
28         Get the top element.
29         :rtype: int
30         """
31         return self.lists[-1]
32 
33     def empty(self):
34         """
35         Returns whether the stack is empty.
36         :rtype: bool
37         """
38         return len(self.lists) == 0