解法一：字符串处理

朴实无华的字符串处理问题，注意考虑和为0的情况。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String[] input = reader.readLine().split(" ");
        int a = Integer.parseInt(input[0]);
        int b = Integer.parseInt(input[1]);
        int c = a + b;
        if (c == 0) {
            System.out.println(0);
            return;
        }
        int temp = Math.abs(c);
        int index = 0;
        StringBuilder sBuilder = new StringBuilder();
        while (temp != 0) {
            if ((index > 0) && (index % 3 == 0)) {
                sBuilder.append(',');
            }
            ++index;
            sBuilder.append(temp % 10);
            temp /= 10;
        }
        if (c < 0) {
            sBuilder.append('-');
        }
        System.out.println(sBuilder.reverse().toString());
    }
}