[LintCode] Restore IP Addresses Show result

public class Solution {
    /**
     * @param s the IP string
     * @return All possible valid IP addresses
     */
    public ArrayList<String> restoreIpAddresses(String s) {
        // Write your code here
        ArrayList<String> result = new ArrayList<String>();
        if (s == null || s.length() < 4 || s.length() > 12) {
            return result;
        }
        helper(s, 0, "", result, 0);
        return result;
    }
   
    private void helper(String s, int start, String tmp, ArrayList<String> result, int points) {
        if (start == s.length() && points == 4) {
            result.add(tmp);
            return;
        }
        for (int i = 1; i <= 3 && start + i <= s.length(); i++) {
            if (Integer.parseInt(s.substring(start, start + i)) <= 255) {
                String tail = s.substring(start, start + i);
                if (!tail.equals(Integer.toString(Integer.parseInt(tail)))) {
                    return;
                }
                if (points != 3) tail += ".";
                helper(s, start + i, tmp + tail, result, points + 1);
            }
        }
    }
}

好久不练，一个dfs写了半小时也是太差T_T

Dec 3

Java RuntimeException serialVersionUID:
http://stackoverflow.com/questions/285793/what-is-a-serialversionuid-and-why-should-i-use-it

Dec 1

Singleton and Prototype:
http://www.studytrails.com/frameworks/spring/spring-singleton-and-prototype.jsp