LeetCode 306. Additive Number

class Solution {
public:
    std::string::size_type sz = 0; 
    bool isAdditiveNumber(string num) {

    for (int i = 0; i < num.length(); i++)
    {
        for (int j = i + 1; j < num.length(); j++)
        {
            if (check(num, i, j))
                return true;
        }
    }

    return false;

}

bool check(string num,int first,int second)
{
    if(num[0]=='0'&&first!=0)
        return false;
    if(num[first+1]=='0'&&second!=first+1)
        return false;
   
    long long int number1 = std::stoll (num.substr(0, first - 0 + 1).c_str(),&sz,0);
    long long int number2 = std::stoll (num.substr(first + 1, second - first).c_str(),&sz,0);

    long long int number3 = number1 + number2;

    int i = second+1,j = 0;
    do
    {
        
        string s = to_string(number3);
        if(num[i]=='0'&&i!=num.length()-1)
            return false;
        for (j = 0; i < num.length() && j < s.length(); i++, j++)
        {
            if (s[j] != num[i])
            {
                return false;
            }
        }
        if (j != s.length())
        {
            return false;
        }
        number1 = number2;
        number2 = number3;
        number3 = number1 + number2;
        first = second;
        second = i - 1;
    }
    while (i < num.length());

    return true;
}
};