856. Score of Parentheses

 

Stack solution:

class Solution {
    public int scoreOfParentheses(String s) {
        Stack<Integer> st = new Stack<>();
        int score = 0;
        for(int i = 0; i < s.length(); i++){
            char ch = s.charAt(i);
            if(ch == '('){
                st.push(score);
                score = 0;
            }
            else {                
                if(score==0)
                    score = 1;
                else
                    score = 2*score;
                score += st.pop();
            }
        }
        return score;
    }
}

Recursive solution:

class Solution {
    int index = 0;
    public int scoreOfParentheses(String s) {
         int score = 0;
        while(index<s.length()){
            char ch = s.charAt(index++);
            if(ch == '('){
                score += scoreOfParentheses(s);
            }
            else {                
                if(score==0)
                    score = 1; 
                else
                    score = 2*score;
                return score;
            }
        }
        return score;
    }
    
  
}