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)

Solution:

注意这里if(tmp < 256 && tmp.toString().equals(s.substring(pos, pos + j)))

如果不加tmp.toString().equals(s.substring(pos, pos + j))， 则可能会出现001 这种情况， 即高位为0.

public class Solution {
    ArrayList<String> result = null;
    public ArrayList<String> restoreIpAddresses(String s) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        result = new ArrayList<String>();
        getAddress(s, 0, 4, new StringBuffer());
        return result;
    }
    public void getAddress(String s, int pos, int num, StringBuffer sb){
        if(num == 0 || pos == s.length()){
            if(pos == s.length() && num == 0){
                result.add(sb.substring(0, sb.length() - 1));
            }
            return;
        }
        for(int j = 1; j < 4 && pos + j <= s.length(); j ++){
            Integer tmp = Integer.valueOf(s.substring(pos, pos + j));
            if(tmp < 256 && tmp.toString().equals(s.substring(pos, pos + j))){
                sb.append(s.substring(pos, pos + j));
                sb.append(".");
                getAddress(s, pos + j, num - 1, sb);
                sb.delete(sb.length() - j - 1, sb.length());
            }
        }
    }
}