链接：20. 有效的括号 - 力扣（LeetCode）

python中list就可以直接当栈用

 1 class Solution(object):
 2     def isValid(self, s):
 3         """
 4         :type s: str
 5         :rtype: bool
 6         """
 7         length = len(s)
 8         help_stack = []
 9         i = 0
10         while i < length:
11             if s[i] == '(' or s[i] == '{' or s[i] == '[':
12                 help_stack.append(s[i])
13             elif s[i] == ')':
14                 if len(help_stack) != 0 and help_stack[-1] == '(':
15                     help_stack.pop()
16                 else:
17                     return False
18             elif s[i] == '}':
19                 if len(help_stack) != 0 and help_stack[-1] == '{':
20                     help_stack.pop()
21                 else:
22                     return False
23             elif s[i] == ']':
24                 if len(help_stack) != 0 and help_stack[-1] == '[':
25                     help_stack.pop()
26                 else:
27                     return False
28             i += 1
29         if len(help_stack) == 0 :
30             return True
31         else:
32             return False