Additive sequence

class Solution {

  public:

bool isAdditiveSequence(string str) {

        // Your code here

        int n = str.size();

        if(n<3)

            return 0;

            

        string ans,s1;

        

        for(int i=0;i<min(n-1,10);i++){

            s1.push_back(str[i]);

            string s2 = "";

            for(int j=i+1;j<min(n,10);j++){

                s2.push_back(str[j]);

                ans = s1+s2;

                int a = stoi(s1);

                int b = stoi(s2);

                while(ans.size()<n){

                    int sum = a+b;

                    string s = to_string(sum);

                    if(n-ans.size() < s.size())

                        break;

                    ans += s;

                    a=b;

                    b=sum;

                    if(ans == str)

                        return 1;

                }

            }

        }

        

        return 0;

}

};