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);
         }
     }

 }