Leetcode-Resotre 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)

Analysis:

This is a recursive problem. A string will be divided into four parts. For each part, we should determine whether it is a valid IP segment.

Solution:

public class Solution {
    public List<String> restoreIpAddresses(String s) {
          List<String> res = new ArrayList<String>();
          if (s.length()==0) return res;

          res = restoreRecur(s,0,4);
          return res;        
    }

    public List<String> restoreRecur(String s, int curIndex, int num){
        List<String> res = new ArrayList<String>();
        if (curIndex>=s.length()) return res;
        
        if (num==1){
           String temp = s.substring(curIndex,s.length());
           if (temp.length()>3) return res;
           int val = Integer.parseInt(temp);
           if (temp.length()==3 && val>=100 && val<=255){
               res.add(temp);
               return res;
           }
           if (temp.length()==2 && val>=10 && val<=99){
               res.add(temp);
               return res;
           }
           if (temp.length()==1){
               res.add(temp);
               return res;
           }
           return res;           
        }
        
        if (curIndex+1>=s.length()) return res;
        int end = curIndex+3;
        if (curIndex+3>s.length())
            end = s.length();
        

        for (int i=curIndex+1;i<=end;i++){
            String temp = s.substring(curIndex,i);
            int val = Integer.parseInt(temp);
            List<String> nextRes = new ArrayList<String>();
            if (temp.length()==3 && val>=100 && val<=255){
                nextRes = restoreRecur(s,i,num-1);               
            }
            if (temp.length()==2 && val>=10 && val<=99){
                nextRes = restoreRecur(s,i,num-1);               
            }
            if (temp.length()==1){
                nextRes = restoreRecur(s,i,num-1);               
            }
            for (int j=0;j<nextRes.size();j++)
                res.add(temp+"."+nextRes.get(j));
        }
        return res;       
        
    } 
}