LintCode: Restore IP Address

C++

string::substr(start_pos, length)

vector::push_back(element)

 class Solution {
 public:
     vector<string> restoreIpAddresses(string s) {
         vector<string> ret;
         if(s.size() > )
             return ret;
         for(int i = ; i < s.size(); i ++)
         {// [0, i]
             string ip1 = s.substr(, i+);
             if ( !check(ip1) ) break;
             for(int j = i+; j < s.size(); j ++)
             {// [i+1, j]
                 string ip2 = s.substr(i+, j-i);
                 if ( !check(ip2) ) break;
                 for(int k = j+; k < s.size()-; k ++)
                 {// [j+1, k], [k+1, s.size()-1]
                     string ip3 = s.substr(j+, k-j);
                     string ip4 = s.substr(k+);
                     if(check(ip3) && check(ip4))
                     {
                         string ip = ip1 + "." + ip2 + "." + ip3 + "." + ip4;
                         ret.push_back(ip);
                     }
                 }
             }
         }
         return ret;
     }
     bool check(string ip)
     {
         int value = stoi(ip);
         if(ip[] == '')    return ip.size() == ;
         return value <=  ? true : false;
     }
 };