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 scanner = new Scanner(System.in);
        while(scanner.hasNext()) {
            String firstStr = scanner.nextLine();
            String secondStr = scanner.nextLine();
            int diffNum = firstStr.length() - secondStr.length();
            if(diffNum > 0)
            {
                for(int i = 0; i < diffNum; i ++)
                {
                    secondStr = "0" + secondStr;
                }
            }else if (diffNum < 0)
            {
                diffNum = Math.abs(diffNum);
                for(int i = 0; i < diffNum; i ++)
                {
                    firstStr = "0" + firstStr;
                }
            }
            int pos1 = firstStr.length() - 1;
            int pos2 = secondStr.length() - 1;
            StringBuilder addSb = new StringBuilder();
            boolean haveCarry = false;
            while(pos1 >=0 && pos2 >= 0)
            {
                char ch1 = firstStr.charAt(pos1);
                char ch2 = secondStr.charAt(pos2);
                int digit1 = ch1 - '0';
                int digit2 = ch2 - '0';
                int addResult = digit1 + digit2;
                if(haveCarry)
                {
                    addResult = addResult + 1;
                    haveCarry = false;
                }
                if(addResult >= 10)
                {
                   haveCarry = true;
                   addResult = addResult - 10;
                }
                addSb.append(addResult);
                pos1 -- ;
                pos2 --;
            }
            if(haveCarry)
            {
                addSb.append(1);
            }
            System.out.println(addSb.reverse());

        }
    }
}