Method minAddToMakeValid

MinAddToMakeStringValid.java:3–18

(String s)

//stack approach
class Solution {
public int minAddToMakeValid(String s) {
        Stack<Character> stack = new Stack<>();
        for(int i=0;i<s.length();i++){
            char ch = s.charAt(i);
            if(ch == '('){
                stack.push(ch);
            } else {
                if(stack.isEmpty() || stack.peek()==')') {
                     stack.push(ch);
                } else {
                    stack.pop();
                }
            }
        }
        return stack.size();
    } 
}

//two pointers