题解 | #动态字符串#

import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String str = scanner.next(); int i=str.length()%3;

    for(int j =0;j<str.length();j++){
        if(str.length()<=3){
            System.out.println(str);
            break;
        }
        else if(i==0){
            System.out.print(str.charAt(j));
            if(j%3==2&&j!=str.length()-1)System.out.print(",");

        }else if(i==1){

            System.out.print(str.charAt(j));
            if(j%3==0&&j!=str.length()-1)System.out.print(",");
        }else if(i==2){
            System.out.print(str.charAt(j));
            if(j%3==1&&j!=str.length()-1)System.out.print(",");

        }
    }
}

}