20. Valid Parentheses(括号匹配，用桟)

Posted 2020-10-25 张乐乐章

Given a string containing just the characters ‘(‘, ‘)‘, ‘{‘, ‘}‘, ‘[‘ and ‘]‘, determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

 

 1 class Solution:
 2     def isValid(self, s):
 3         """
 4         :type s: str
 5         :rtype: bool
 6         """
 7         stack = []
 8         d={‘(‘:‘)‘,‘[‘:‘]‘,‘{‘:‘}‘}
 9         for i in s:
10             if i in d.keys():#遇到左括号 压桟
11                 stack.append(i)
12             else: #遇到右括号
13                 if stack ==[]:  #桟为空，没有匹配的
14                     return False
15                 else:
16                     if i==d[stack[-1]] : #如果匹配上，弹桟
17                         stack.pop()
18                     else:
19                         return False #没有匹配上
20         return stack==[] #如果遍历完之后桟为空，则全部匹配
21                 
22         
23