public static int gemstones(List<String> arr) {
    // Write your code here
    int count=0; 
    String alphabet = "abcdefghijklmnopqrstuvwxyz";
    for (int i = 0; i < alphabet.length(); i++) {
        boolean flag = true;
        for (String str : arr) {
            if(!str.contains(String.valueOf(alphabet.charAt(i)))){
                flag = false;
            }
        }
        if (flag) {
            count++;
        }
    }
    
    return count;

    }