private List<String> find(int n, boolean original) {
        if (n == 0) return Arrays.asList("");
        if (n == 1) return Arrays.asList("0", "1", "8");

        List<String> res = new ArrayList<String>();
        List<String> list = find(n - 2, false);
        for (String num : list) {
            if (!original) res.add("0" + num + "0");
            res.add("1" + num + "1");
            res.add("6" + num + "9");
            res.add("8" + num + "8");
            res.add("9" + num + "6");
        }
        return res;
    }