题解 | #字符个数统计#

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

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
		// 用Set做去重
        HashSet<Integer> numbers = new HashSet<Integer>();

        String input = "";
        while (in.hasNext()) { 
            input = in.next();
        }

        for (int i =0; i< input.length();i++){
			// 强制类型转换，将char转换成int，这里用到了ASCII字符集
            int current = (int) input.charAt(i);
		  	题干里0-127的限制应该是因为ASCII范围是 0 到 127，ASCII不包含的字符，Java会用Unicode（例如UTF-16）字符集进行转换
            if(current>=0 && current<=127){
                numbers.add(current);
            }
        }
        Integer result = numbers.size();
        System.out.println(result);
    }
}