class Solution {
    public int maxLength(List<String> val) {
        int[] arr = new int[val.size()];
        for (int i = 0; i < val.size(); ++i) arr[i] = stringToBitmask(val.get(i));

        return check(arr, 0, 0, 0);
    }

    private int stringToBitmask(String str) {
        char[] arr = str.toCharArray();
        int mask = 0;
        for (char item : arr) {
            if ((mask & (1 << item - 'a')) > 0) return 0;
            mask += 1 << (item - 'a');
        }

        return mask;
    }

    private int check(int[] items, int me, int position, int max) {
        for (int i = position; i < items.length; ++i) {
            if ((me & items[i]) > 0) {
                continue;
            }
            max = Math.max(max, check(items, me + items[i], i + 1, Math.max(max, Integer.bitCount(me + items[i]))));
        }

        return max;
    }
}