题解 | #数组倒转# JAVA29 动态字符串

import java.util.ArrayList;

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

        //write your code here......
        StringBuffer sb = new StringBuffer();
        int cnt = 0;
        for (int i = str.length() - 1; i >= 0; i--) {
            sb.append(str.charAt(i));
            cnt++;
            if(cnt % 3 == 0 && i != 0)  {
                sb.append(",");
            }
        }
        System.out.println(sb.reverse());
    }
    
    public static void main1(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        //write your code here......
        StringBuffer sb = new StringBuffer(str);
        for (int i = str.length() - 3; i >= 0; i -= 3) {
            sb.insert(i, ",");
        }
        System.out.println(sb);
    }
}