public  static void perm(String s) {
           alternativePerm("", s);
    }

    public static void alternativePerm(String prefix, String s) {
        if (s.length() == 0) {
            System.out.println(prefix);
        }
        for (int i=0; i<s.length(); i++) {
            alternativePerm(prefix+s.charAt(i), s.substring(0,i) + s.substring(i+1, s.length()));
        }
    }