请设计一个算法能够完成两个用字符串存储的整数进行相加操作，对非法的输入则返回error

输入描述:

输入为一行，包含两个字符串，字符串的长度在[1,100]。

输出描述:

输出为一行。合法情况输出相加结果，非法情况输出error

Java解法：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class test04 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] str = br.readLine().split(" ");
        String result = add(str[0], str[1]);
        System.out.println(result);
    }

    private static String add(String s, String s1) {
        char [] c1 = s.toCharArray();
        char [] c2 = s1.toCharArray();
        if (!check(c1) || !check(c2)) {
            return "error";
        }
        if (c1.length < c2.length) {
            char [] temp = c1;
            c1 = c2;
            c2 = temp;
        }
        int plus = 0;
        int i = c1.length - 1, j = c2.length - 1;
        while (j >= 0) {
            int temp = c1[i] - ‘0‘ + c2[j] - ‘0‘ + plus;
            plus = temp / 10;
            c1[i] = (char)(temp % 10 + ‘0‘);
            i--;
            j--;
        }
        while (i >= 0 && plus > 0) {
            int temp = c1[i] - ‘0‘ + plus;
            plus = temp / 10;
            c1[i] = (char)(temp % 10 + ‘0‘);
            i--;
        }
        StringBuilder str = new StringBuilder();
        if (plus > 0) {
            str.append(‘1‘);
        }
        for (char c : c1) {
            str.append(c);
        }
        return str.toString();
    }

    private static boolean check(char[] c) {
        for (char aC : c) {
            if (aC < ‘0‘ || aC > ‘9‘) {
                return false;
            }
        }
        return true;
    }
}