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> solutions = new ArrayList<String>();
    restoreIp(s, solutions, 0, "", 0);
    return solutions;
}

private void restoreIp(String ip, List<String> solutions, int idx, String restored, int count) {
    if (count > 4) return;
    if (count == 4 && idx == ip.length()) solutions.add(restored);

    for (int i=1; i<4; i++) {
        if (idx+i > ip.length()) break;
        String s = ip.substring(idx,idx+i);
        if ((s.startsWith("0") && s.length()>1) || (i==3 && Integer.parseInt(s) >= 256)) continue;
        restoreIp(ip, solutions, idx+i, restored+s+(count==3?"" : "."), count+1);
    }
}
}