public static int gemstones(List<String> arr) {
    Map<String, Long> countmap = arr.stream().map(s -> s.split("")).map(Arrays::stream)
            .map(stream -> {
                Set<String> set = new HashSet<>();
                stream.forEach(set::add);
                return set;
            }).
            flatMap(Set::stream).
            collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
    return (int)countmap.entrySet().stream().filter(en -> en.getValue() == arr.size()).count();
}