Restore IP Addresses (Java)

LeetCode

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)

Solution:

DFS to combine each possible result, meanwhile skip all impossible combination for result, such as

rest letters in s can not be more than 3* rest parts and rest letters can not be less than rest parts.