Get value from Parenthesis

/*
Given a parenthesis string consisting of ' ( ' , ' ) ' and integers (integers will be in the range from -109 to 109), you have to get the value of the string by following rules:

There is always an integer between an opening and a closing parenthesis.
(x) gives absolute value of x.
If there are consecutive balanced parenthesis, then you have to alternatively add and subtract them, i.e. if the string is (x)(y)((z)) then value of this string will be - ( value got from (x) ) - ( value got from (y) ) + ( value got from ((z)) )
Example 1:

Input:
s = "(((1)))"
Output:
1
Explanation: Steps:
1. (((1))) = ((abs(1))) = ((1))
2. ((1)) = (abs(1)) = (1)
3. (1) = abs(1) = 1
Example 2:

Input:
s = "((-1)(3))"
Output:
2
Explanation: Steps:
1. ((-1)(3)) = (abs(-1) - abs(3)) = 
   (1 - 3) = (-2)
2. (-2) = abs(-2) = 2

Your Task:
You don't need to read input or print anything. Your task is to complete the function getValue() which takes the string s as input parameter and returns the value got by solving parenthesis.

Constraints:
1 ≤ |s| ≤ 106
*/

//User function Template for C++

class Solution{
    public:
    long long getValue(string s){
        stack<long long> st;
        for(int i = 0; i < s.length(); i++){
            if(s[i] == '('){
                st.push(1e18);
            }
            else if(s[i] == ')'){
                long long cur = 0;
                long long val = 0;
                while(st.top() < 1e18){
                    if(cur % 2){
                        val -= (long long )st.top();
                        st.pop();
                    }
                    else{
                        val += (long long )st.top();
                        st.pop();
                    }
                    cur++;
                }
                st.pop();
                st.push(abs(val));
            }
            else{
                string r;
                while(s[i] != ')' && s[i] != '('){
                    r.push_back(s[i]);
                    i++;
                }
                long long val;
                if(r[0] == '-'){
                    r.erase(r.begin());
                    val = stoi(r);
                    val = -val;
                }
                else{
                    val = stoi(r);
                }
                st.push(val);
                i--;
            }
        }
        long long cur = 0;
        long long val = 0;
        while(st.size()){
            if(cur % 2){
                val -= (long long )st.top();
                st.pop();
            }
            else{
                val += (long long )st.top();
                st.pop();
            }
            cur++;
        }
        return abs(val);
    }
};