Counting unique characters in a String given by the user

Question

I have to write a program that counts the uniques characters in a String given by the user. For example \"abc\" returns 3 and \"aabbccd\" returns 4. I am not allow to use advan

Answer 1

public static int countUniqueChars (String buf) {
    HashSet hash = new HashSet<>();
    buf = buf.toUpperCase();
    for (int i = 0; i < buf.length(); i++)
        hash.add(buf.charAt(i));
    return hash.size();
}