# 2116. Check if a Parentheses String Can Be Valid
###### tags: `Leetcode` `Medium` `Parentheses`
Link: https://leetcode.com/problems/check-if-a-parentheses-string-can-be-valid/description/
## 思路
思路参考[这里](https://leetcode.com/problems/check-if-a-parentheses-string-can-be-valid/solutions/1646594/left-to-right-and-right-to-left/)
先从左到右扫描看有没有孤儿')'
再从右到左扫描看有没有孤儿'('
## Code

class Solution:
    def canBeValid(self, s: str, locked: str) -> bool:

        def validate(s: str, locked: str, op: str) -> bool:
            lockedScore = 0
            unlockedCnt = 0
            for i in range(len(s)):
                if locked[i]=="1":
                    lockedScore += 1 if s[i]==op else -1
                else:
                    unlockedCnt += 1
                if lockedScore+unlockedCnt<0: 
                    return False
            return unlockedCnt>=lockedScore
        
        return len(s)%2==0 and validate(s, locked, '(') and validate(s[::-1], locked[::-1], ')')