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class Solution {
public:
    vector<string> restoreIpAddresses(string s) {
        vector<string> ans;
        ans.clear();
        if(s.length() > 12)return ans;
        vector<int> split;
        split.clear();
        split.push_back(0);
        for(int i = 0;i < s.length();i++) {
            int num = genInt(split[split.size()-1],i,s);
            if(num >= 0&&num <= 255) {
                split.push_back(i);
                searchS(s,split,ans);
                split.pop_back();
            }
        }
        return ans;
    }
private:
    int genInt(int start,int end,string s) {
        string numstr(s,start,end-start+1);
        if(numstr.length() >= 4)return -1;
        if(end > start && s[start] == '0')return -1;
        int num = 0;
        bool flag = false;
        for(int i = numstr.length()-1;i >= 0;i--) {
            flag = true;
            num += (numstr[i] - '0')*(int)pow(10.0,(int)numstr.length() - 1 - i);
        }
        if(!flag)return -1;
        return num;
    }
    void searchS(string s,vector<int>& split,vector<string>& ans) {
        if(split.size() == 5) {
            string tmp = s;
            for(int i = 1;i < split.size()-1;i++) {
                tmp.insert(tmp.begin()+split[i]+i,'.');
            }
            ans.push_back(tmp);
            return;
        }
        if(split.size() == 4) {
            int numlast = genInt(split[split.size()-1]+1,s.length()-1,s);
            if(numlast >= 0&&numlast <= 255) {
                split.push_back(s.length()-1);
                searchS(s,split,ans);
                split.pop_back();
            }
            return;
        }
        for(int i = split[split.size()-1]+1;i < s.length();i++) {
            int num = genInt(split[split.size()-1]+1,i,s);
            if(num >= 0&&num <= 255) {
                split.push_back(i);
                searchS(s,split,ans);
                split.pop_back();
            }
        }
    }
};