题解 | #高精度整数加法#

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);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            String as = in.nextLine();
            String bs = in.nextLine();
            StringBuilder out = new StringBuilder();//用于存放相加后的结果
            int l = Math.max(as.length(), bs.length());
            int subl = Math.abs(as.length() - bs.length());
		  //as 和 bs 长度不等时，短的那个前面补0
            if (subl != 0) {
                String sub0 = "";
                for (int j = 0; j < subl; j++) {
                    sub0 = sub0.concat("0");
                }
                if (as.length() > bs.length()) {
                    bs = sub0.concat(bs);
                } else if (bs.length() > as.length()) {
                    as = sub0.concat(as);
                }
            }

            int pre = 0; //存放单数字相加结果的十位数，为0或1;
            for (int i = l - 1; i >= 0; i--) {
                char ai = as.charAt(i);
                char bi = bs.charAt(i);
                int num = ai - '0' + bi - '0' + pre;
                pre = 0;
                int num0 = num % 10;
                if (i == 0) {
                    out.insert(0, Integer.toString(num));
                    break;
                }
                if (num >= 10) {
                    out.insert(0, Integer.toString(num0));
                    pre += 1;
                } else if (num < 10) {
                    out.insert(0, Integer.toString(num0));
                }
            }
            System.out.println(out.toString());
        }
    }
}