题目
A parentheses string is valid if and only if:
- It is the empty string,
- It can be written as AB (A concatenated with B), where A and B are valid strings, or
-
It can be written as (A), where A is a valid string. You are given a parentheses string s. In one move, you can insert a parenthesis at any position of the string.
- For example, if s = “()))”, you can insert an opening parenthesis to be “(()))” or a closing parenthesis to be “())))”. Return the minimum number of moves required to make s valid.
解题思路
记录所需的右括号个数，如果遇到左括号，需要的个数+1，遇到右括号，如果需要则需要的-1，否则结果+1，最后结果加上所有的右括号个数
代码
class Solution:
def minAddToMakeValid(self, s: str) -> int:
res = bal = 0
for c in s:
if c == "(":
bal += 1
elif bal:
bal -= 1
else:
res += 1
return res + bal
