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();

        //write your code here......
        int startIndex = str.length() % 3;
        System.out.print(str.substring(0, startIndex));
        for(int i = startIndex; i < str.length(); ){
            if(i + 3 > str.length()){
                System.out.print("," + str.substring(i));
                break;
            }
            System.out.print("," + str.substring(i, i + 3));
            i += 3;
        }
    }
}