check if a parentheses string can be valid

A parentheses string is a non-empty string consisting only of '(' and ')'. It is valid if any of the following conditions is true:

It is ().
It can be written as AB (A concatenated with B), where A and B are valid parentheses strings.
It can be written as (A), where A is a valid parentheses string.


//c++ code 

class Solution {
public:
    bool canBeValid(string s, string locked) {
    
    int n = s.length();
    if (n % 2 != 0) return false;
    int openUnlocked = 0, balance = 0;
    for (int i = 0; i < n; ++i) {
        if (locked[i] == '0') ++openUnlocked;
        else if (s[i] == '(') ++balance;
        else --balance;
        if (balance < -openUnlocked) return false;
    }
    openUnlocked = 0; balance = 0;
    for (int i = n - 1; i >= 0; --i) {
        if (locked[i] == '0') ++openUnlocked;
        else if (s[i] == ')') ++balance;
        else --balance;
        if (balance < -openUnlocked) return false;
    }
    return true;
    }
};