bool isAdditiveNumberHelper(string &num, int start, string &first, string &second) {
if(start+first.size()+second.size() == num.size()) return true;
string answer = add(first,second);
if(num.substr(start+first.size()+second.size(), answer.size()) != answer) return false;
return isAdditiveNumberHelper(num, start + first.size(),second, answer);
}
bool isAdditiveNumberHelper(string& n1, string& n2, string& n3){
string add = StringAdd(n1, n2);
if (add.size() > n3.size()) return false;
if (add == n3 ) return true;
//split the n3 to 2 parts, and keep going.
string cut = n3.substr(0, add.size());
if (add == cut) {
string rest = n3.substr(add.size());
return isAdditiveNumberHelper(n2, add, rest);
}
return false;
}
bool isAdditiveNumber(string num) {
int len = num.size();
for(int i=1; i<len/2+1; i++) {
string n1 = num.substr(0, i);
if ( n1.size()>1 && n1[0] == '0') break;
for(int j=i+1; j<len; j++) {
string n2 = num.substr(i, j-i);
if ( n2.size()>1 && n2[0] == '0') break;
string n3 = num.substr(j);
if (isAdditiveNumberHelper(n1, n2, n3)) return true;
}
}
return false;
}
bool isAdditiveNumber(string num) {
string first;
for(int i = 0; i < int(num.size())-2; ++i) {
first += num[i];
if(first.size()>1&&first[0] == '0') break;
string second;
for(int j = i+1; j < int(num.size())-1; ++j) {
second += num[j];
if(second.size()>1&&second[0] == '0') break;
if(isAdditiveNumberHelper(num, 0,first, second)) return true;
}
}
return false;
}
