Python3解leetcode Valid Parentheses

问题描述：

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

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.

Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true

Example 2:

Input: "()[]{}"
Output: true

Example 3:

Input: "(]"
Output: false

Example 4:

Input: "([)]"
Output: false

Example 5:

Input: "{[]}"
Output: true

解题思路及方法：利用字典进行各个符号之间的配对；利用stack的先进后出特性进行验证

代码：

 1 class Solution:
 2     def isValid(self, s: str) -> bool:
 3         if len(s)%2 != 0: return False
 4         b = {'(':')', '[':']', '{':'}'}
 5         stack = []
 6         for x in s:
 7             if x in b:
 8                 stack.append(x)
 9             else:
10                 if stack and x==b[stack.pop()]:
11                     continue
12                 else :
13                     return False
14         if stack:
15             return False
16         else:
17             return True
18