public  long factorial(int number) {
        long result = 1;

        for (int factor = 2; factor <= number; factor++) {
            result *= factor;
        }

        return result;
    }
    public String[] unRank(String set, int n)
    {
        String res[] = new String[set.length()];
        while (set.length() > 0)
        {
            int setSize = (int) factorial(set.length()-1);
            int index = n/setSize;
            res+=set.charAt(index);
            set = index > 0 ? set.substring(0, index) : "" +
                  (index < set.length()-1) != null ? set.substring(index+1) : "";

            n = n % setSize;
        }
        return res;
    }