题解 | 添加逗号

import java.util.Scanner;

// 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 s = in.nextLine();
        int n = s.length();
        if (n % 3 == 0) {
            for (int i = 0; i < n; i++) {
                System.out.print(s.charAt(i));
                if ((i + 1) % 3 == 0 && (i + 1) != n) {
                    System.out.print(",");
                }
            }
        } else {
            int a = n % 3;
            for (int i = 0; i < a; i++) {
                System.out.print(s.charAt(i));
            }
            if(n/3!=0){
                System.out.print(",");
            }
            
            for (int i = a; i < n; i++) {
                System.out.print(s.charAt(i));
                if ((i + 1-a) % 3 == 0 && (i + 1) != n) {
                    System.out.print(",");
                }
            }
        }
    }
}