247. Strobogrammatic Number II

A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Find all strobogrammatic numbers that are of length = n.

For example,
Given n = 2, return["11","69","88","96"].

    public List<String> findStrobogrammatic(int n) {
        List<String> res = new ArrayList<>((n & 1) == 0 ? Arrays.asList("") : Arrays.asList("0", "1", "8"));
        if (n < 2) {
            return res;
        }

        for (int i = n % 2 + 2; i <= n; i += 2) {
            List<String> cur = new ArrayList<>();
            for (String s : res) {
                if (i != n) {
                    cur.add("0" + s + "0");
                }
                cur.add("1" + s + "1");
                cur.add("6" + s + "9");
                cur.add("8" + s + "8");
                cur.add("9" + s + "6");
            }
            res = cur;
        }
        return res;
    }