class Solution {
public:
    vector<string> restoreIpAddresses(string s) {

        str=s;
        result.clear();
        vector<string> t;
        if(s.size()>12)
        {
            return t;
        }
        deal(0,4);

        for(auto&& a:result)
        {
            string n;
            for(auto num:a)
            {
                n+=to_string(num);
                n+='.';
            }
            n.pop_back();
            t.push_back(n);
        }
        return t;
    }

    int valid(int i,int j)
    {
        string t(str.begin()+i,str.begin()+j+1);
        //cout<<t<<endl;
        if(t.front()=='0'&&t.size()!=1)
            return -1;
        return std::stoi(t);
    }

    void deal(int begin,int remain)
    {
        if(remain==0&&begin==str.size())
        {
            result.push_back(address);
            return;
        }

        for(int i=begin;i<begin+3&&i<str.size();++i)
        {
            auto num=valid(begin,i);
            if(remain==4)
                address.clear();
            if(num>=0&&num<=255)
            {
                address.push_back(num);
                deal(i+1,remain-1);
                address.pop_back();
            }
        }
    }

    vector<vector<int>> result;
    vector<int> address;
    string str;
};