ip_address.cpp

/*
Using simple three loops
*/

class Solution {
public:
        long int stoi(string s){
                long int num = 0;
                for(int i=0;i<s.length();i++)
                        num = (num * 10) + (int)(s[i] - '0');
                return num;
        }

        bool isvalid(string temp){
                if(temp.length() > 1 and temp[0] == '0') return false;
                if(stoi(temp) <= 255 && stoi(temp) >= 0) return true;
                else return false;
        }

        vector<string> restoreIpAddresses(string s) {
                if(s.length() > 12 && s.length() < 4)
                        return result;
                for(int i=1; i<4; i++){
                        string first = s.substr(0,i);
                        if(!isvalid(first)) continue;
                        for(int j=1; i+j<s.length() && j<4; j++){
                                string second = s.substr(i,j);
                                if(!isvalid(second)) continue;
                                for(int k=1; i+j+k < s.length() && k<4; k++){
                                        string third = s.substr(i+j,k);
                                        string fourth = s.substr(i+j+k);
                                        if(isvalid(third) && isvalid(fourth)){
                                                string temp = first + "." + second + "." + third + "." + fourth;
                                                result.push_back(temp);
                                        }
                                }
                        }
                }
                return result;
        }
private:
        vector<string> result;
};