Leetcode（93）： Restore IP Addresses

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)

public class Solution {
    public List<String> restoreIpAddresses(String s) {
           List<String> res=new ArrayList<String>();
           if(s.length()<4||s.length()>12) return res;
           dfs(s,"",res,0);
           return res;
        }
       public static void dfs(String s,String temp,List<String> list,int count){
           if(count==3&&isValid(s)){
               list.add(temp+s);
               return;
           }
           for(int i=1;i<4&&i<s.length();i++){
               String substr=s.substring(0,i);
               if(isValid(substr)){
                   dfs(s.substring(i),temp+substr+".",list,count+1);
               }
           }
       }
       
       public static boolean isValid(String s){
           if(s.charAt(0)=='0') return s.equals("0");
           int num=Integer.parseInt(s);
           return num<=255&&num>0;
       }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc=new Scanner(System.in);
        solution sl=new solution();
        
        List<String> list=sl.restoreIpAddresses(sc.next());
        
        for(String i:list){
            System.out.println(i);
        }
    }

}