class Solution {public:    vector<string> restoreIpAddresses(string s) {        vector<string> res;        int len = s.size();        if(len<4)            return res;        for(int i=0;i<len-2;i++)            for(int j=i+1;j<len-1;j++)                for(int k=j+1;k<len;k++){                    if(i-0<=3 && j-i<=3 && k-j<=3){                                             string sRestore =IsValidAndRestore(i,j,k,s);                     if(sRestore != "" && find(res.begin(),res.end(),sRestore)==res.end())                       res.push_back(sRestore);                    }                                                }//end for    return res;    }private:        bool valid(string s){//各子串是否合法       istringstream is(s);       int res;       is>>res;              if((s.size()>1 && s[0]==‘0‘)|| res>255 || res<0)           return false;       else           return true;           }//end valid    string IsValidAndRestore(int x,int y,int z,string s){        string s1 = s.substr(0,x);        string s2 = s.substr(x,y-x);        string s3 = s.substr(y,z-y);        string s4 = s.substr(z);        string Res;        if(valid(s1) && valid(s2) && valid(s3) && valid(s4)){           return s1+"."+s2+"."+s3+"."+s4;        }        return Res;    }//end IsValid};