1.1

UniqueString.java

/**
 * Created by Readman on 6/15/14.
 */
public class UniqueString {
    /*
    time: N, traverse all char in String
    space: since boolean [] take up to 256 (assume ascii) 1
    * */
    public static boolean uniqueString (String s) {
        return rec(s, new boolean[256]);
    }
    public static boolean rec (String s, boolean[] test) {
        if (s.isEmpty()) {
            return  true;
        }
        if (test[s.charAt(0)])
        {
            return false;
        }
        else {
            test[s.charAt(0)] = true;
        }

        return rec (s.substring(1), test);
    }

    public static void main(String[] args) {
        String s = "";
        System.out.println(uniqueString(s));
    }
}