class Solution {public:    vector<string> restoreIpAddresses(string s) {        vector<string> result;        vector<string> ip;        if(s.length() < 4 || s.length() > 12) return result;        dfs(result, ip, s, 1);        return result;    }    void dfs(vector<string> & result, vector<string> &ip, string s, int level){        if(level == 4){            if(s.length() > 3 || s[0] == ‘0‘&& s.length() != 1) return;            if(atoi(s.c_str()) >255) return;            ip.push_back(s);            string tmp;            for(auto i = ip.begin(); i != ip.end(); i++)                tmp += *i + ".";            tmp.pop_back();            result.push_back(tmp);            ip.pop_back();        }else{            if(s[0] == ‘0‘){                ip.push_back("0");                if(s.length() > 1)dfs(result, ip, s.substr(1), level+1);                ip.pop_back();            }else{                for(int i = 1; i <=3 && i < s.length(); i++){                    string tmp = s.substr(0,i);                    if(atoi(tmp.c_str()) <= 255){                        ip.push_back(tmp);                        dfs(result, ip, s.substr(i), level+1);                        ip.pop_back();                    }                }            }        }    }};