题解 | #整数加法#

import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);

        while(in.hasNext()){
            solution(in);
        }
    }

    /**
     * 模拟法
     * @param in
     */
    private static void solution(Scanner in){
        String[] nums = in.nextLine().split(" ");
        String num0 = nums[0];
        String num1 = nums[1];

        if(num0.matches("\\d+") && num1.matches("\\d+")){
            StringBuilder sb = new StringBuilder();
            normalAdder(sb, num0, num1);
            System.out.println(sb);
        }else{
            System.out.println("error");
        }
    }

    /**
     * 两个字符串 对位相加
     * @param sb
     * @param num0
     * @param num1
     */
    private static void normalAdder(StringBuilder sb, String num0, String num1){
        int len0 = num0.length();
        int len1 = num1.length();
        int lenMin = Math.min(len0, len1);

        int carry = 0;
        int sum;
        int remainder;
        for(int i=1; i<=lenMin; i++){
            char ch0 = num0.charAt(len0-i);
            char ch1 = num1.charAt(len1-i);
            sum = carry + Integer.parseInt(String.valueOf(ch0)) + Integer.parseInt(String.valueOf(ch1));
            carry = sum/10;
            remainder = sum%10;
            sb.insert(0, remainder);
        }

        if(len0 == len1){
            if(carry > 0){
                sb.insert(0, carry);
            }
        }else{
            if(len0 > lenMin){
                singleAdder(sb, num0, lenMin, len0, carry);
            }
            if(len1 > lenMin){
                singleAdder(sb, num1, lenMin, len1, carry);
            }
        }
    }

    /**
     * 单个字符串 多余部分与进位相加
     * @param sb
     * @param num
     * @param lenMin
     * @param lenMax
     * @param carry
     */
    private static void singleAdder(StringBuilder sb, String num, int lenMin, int lenMax, int carry){
        int sum, remainder;
        for(int i=lenMin+1; i<=lenMax; i++){
            char ch = num.charAt(lenMax-i);
            sum = carry + Integer.parseInt(String.valueOf(ch));
            carry = sum/10;
            remainder = sum%10;
            sb.insert(0, remainder);
        }
        if(carry > 0){
            sb.insert(0, carry);
        }
    }
}