[leetcode]Restore IP Addresses

DFS所有可能。。。

class Solution {
public:
    void search(const string& s , vector<string>& ans , int step , const string& ip , int start){
        if(s.size() == start && step == 4){
            ans.push_back(ip.substr(1 , ip.size()-1));  
           // cout << ip.substr(1 , ip.size()-1) <<endl;
        }
        
        if(s.size() <= start)
        {
            return;
        }
        //enumation 
        //length 1,2,3
        //1
       // cout << step << " "<< ip << endl;
        if(start < s.size())
        {
           // cout << "get in" <<endl;
            string tip = s.substr(start,1);
          //  cout<< tip << endl;
            search(s , ans , step + 1 , ip + "." + tip , start + 1);
        }
        //2
   
        if(start + 1 < s.size()){
            string tip = s.substr(start,2);
            if(tip[0] != '0') search(s , ans , step + 1 , ip + "." + tip , start + 2);
        }
        //3
        if(start + 2 < s.size()){
            string tip = s.substr(start,3);
            stringstream ss;
            ss << tip;
            int n;
            ss >> n;
            if(n>=100 && n <= 255) search(s , ans , step + 1 , ip + "." + tip , start + 3);
        }
    }
    vector<string> restoreIpAddresses(string s) {
        vector<string> ans;
        if(s.size() > 3*4) return ans;
        search(s , ans , 0 , "" , 0);
        return ans;
    }
};