题解 | #字符个数统计#

import java.util.Scanner;
import java.util.HashSet;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str = in.nextLine();
        char[] chars = str.toCharArray();
        HashSet<Character> set = new HashSet<>();
        int count = 0;
        for (char c : chars) {
            if (set.add(c)) {
                count++;
            }
        }
        System.out.println(count);
    }
}