921. Minimum Add to Make Parentheses Valid

class Solution {
    public int minAddToMakeValid(String s) {
        int open = 0; // unmatched '('
        int add = 0;  // unmatched ')'
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(') {
                open++;
            } else {
                if (open > 0) {
                    open--;
                } else {
                    add++;
                }
            }
        }
        return add + open;
    }
}

class Solution:
    def minAddToMakeValid(self, s: str) -> int:
        open_count = 0
        add = 0

        for c in s:
            if c == '(':
                open_count += 1
            else:
                if open_count > 0:
                    open_count -= 1
                else:
                    add += 1

        return add + open_count

class Solution {
public:
    int minAddToMakeValid(string s) {
        int open = 0;
        int add = 0;

        for (char c : s) {
            if (c == '(') {
                open++;
            } else {
                if (open > 0) {
                    open--;
                } else {
                    add++;
                }
            }
        }

        return add + open;
    }
};

class Solution {
    minAddToMakeValid(s) {
        let open = 0;
        let add = 0;

        for (const c of s) {
            if (c === '(') {
                open++;
            } else {
                if (open > 0) {
                    open--;
                } else {
                    add++;
                }
            }
        }

        return add + open;
    }
}