超长正整数相加

题目描述
请设计一个算法完成两个超长正整数的加法。
输入描述:
输入两个字符串数字
输出描述:

输出相加后的结果，string型

思路一：

import java.math.BigInteger;
import java.util.Scanner;

public class Main
{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext())
        {
            BigInteger n1 = scanner.nextBigInteger();
            BigInteger n2 = scanner.nextBigInteger();
            System.out.println(n1.add(n2));
        }
    }
}

思路二：

import java.util.Scanner;

public class Main
{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext())
        {
            String num1 = scanner.next();
            String num2 = scanner.next();
            StringBuffer sb = new StringBuffer();
            while (num1.length() < num2.length())
                num1 = "0" + num1;
            while (num1.length() > num2.length())
                num2 = "0" + num2;
            int carry = 0;
            int tmp = 0;
            for (int i = num1.length() - 1; i >= 0; i--)
            {
                tmp = num1.charAt(i) - '0' + num2.charAt(i) - '0' + carry;
                if (tmp >= 10)
                {
                    carry = tmp / 10;
                    tmp = tmp % 10;
                }
                else
                    carry = 0;
                sb.append(tmp);
            }
            if (carry > 0)
                sb.append(carry);
            System.out.println(sb.reverse().toString());
        }
    }
}

import java.util.Scanner;

public class Main
{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext())
        {
            String num1 = scanner.next();
            String num2 = scanner.next();
            int resLen = Math.max(num1.length(), num2.length()) + 1;
            char[] res = new char[resLen];
            while (num1.length() < num2.length())
                num1 = "0" + num1;
            while (num1.length() > num2.length())
                num2 = "0" + num2;
            int carry = 0;
            int tmp = 0;
            int index = resLen;
            String result = "";
            for (int i = num1.length() - 1; i >= 0; i--)
            {
                tmp = num1.charAt(i) - '0' + num2.charAt(i) - '0' + carry;
                if (tmp >= 10)
                {
                    carry = tmp / 10;
                    tmp = tmp % 10;
                }
                else
                    carry = 0;
                res[--index] = (char) (tmp + '0');
            }
            if (carry > 0)
            {
                res[--index] = (char) (carry + '0');
                result = String.valueOf(res);
            }
            else
            {
                res[--index] = '0'; //必须赋值
                result = String.valueOf(res).substring(1);
            }

            System.out.println(result);
        }
    }
}