LeetCode - Minimum Add to Make Parentheses Valid

Given a string S of '(' and ')' parentheses, we add the minimum number of parentheses ( '(' or ')', and in any positions ) so that the resulting parentheses string is valid.

Formally, a parentheses string is valid if and only if:

It is the empty string, or
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.
Given a parentheses string, return the minimum number of parentheses we must add to make the resulting string valid.

 

Example 1:

Input: "())"
Output: 1
Example 2:

Input: "((("
Output: 3
Example 3:

Input: "()"
Output: 0
Example 4:

Input: "()))(("
Output: 4
 

Note:

S.length <= 1000
S only consists of '(' and ')' characters.

 

class Solution {
    public int minAddToMakeValid(String S) {
        if (S == null || S.length() == 0) {
            return 0;
        }
        int minLeft = 0;
        int minRight = 0;
    
        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) == '(') {
                minRight++;
            }
            if(S.charAt(i) == ')') {
                if(minRight == 0) {
                    minLeft ++;
                }
                else {
                    minRight --;
                }
            }
        }
        return minLeft + minRight;
    }
}