resotreIpAddress

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

For example:
Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

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#include <string>
#include <vector>
using namespace std;
class Solution {
public:
    vector<string> restoreIpAddresses(string s) {  
        vector<string> result;
        vector<int> path;
        dfs(s,0,0,path,result);
        return result;
    }
private:
    void dfs(string& s,int start,int num,
        vector<int>& path,vector<string>& result){
        if(num == 3) {
            string str = s;
            for(int i=0;i<3;i++){    
                str.insert(path[i]+i,1,'.');
            }
            result.push_back(str);
            return;
        }

        for(int i=1;i<4;i++){
            if((start+i)<s.length() && 3-num<=s.substr(start+i).length() && s.substr(start+i).length()<=(3-num)*3){
                if(stoi(s.substr(start,i))<=255){
                    if(i>1 && s[start] =='0') break;
                    if(num==2 && stoi(s.substr(start+i))>255) continue;
                    if(num==2 && s.substr(start+i).length()>1 && s[start+i]=='0') continue;

                    if(path.empty()) path.push_back(i);
                    else path.push_back(path.back()+i);
                     dfs(s,start+i,num+1,path,result);
                     path.pop_back();
                }
            }
        }
    }
};
int main(){
    string IPaddress="1203045";
    Solution s;
    vector<string> result;
    result = s.restoreIpAddresses(IPaddress);
    return 0;
}