java 代码

import java.io.*;
import java.util.*;
class Main{
    public static void main(String[] args) throws Exception{
         BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));//读取系统的输入
         String[] num1 = reader.readLine().split(" ");
         String[] num2 = reader.readLine().split(" ");
         List<Integer> a = new ArrayList<>();
         List<Integer> b = new ArrayList<>();
         String as = num1[0];
         String bs = num2[0];
         for(int i = 0;i < num1[0].length();i++){
             a.add(as.charAt(i) - '0');
         }
         for(int i = 0;i < bs.length();i++){
             b.add(bs.charAt(i) - '0');
         }
         if(a.size() < b.size()){
             System.out.println("-"+SUB(a,b));
         }else if(a.size() == b.size()){
            if(a.get(0) < b.get(0)){
              System.out.println("-"+SUB(a,b));
            }else{
               System.out.println(SUB(a,b)); 
            }
        }else{
             System.out.println(SUB(a,b)); 
        }
    }
    public static String SUB(List<Integer> a, List<Integer> b){
        if(a.size() < b.size()) return SUB(b,a);
        else if(a.size() == b.size()){
            if(a.get(0) < b.get(0)){
                return SUB(b,a);
            }
        }
        StringBuilder sb = new StringBuilder();
        int tmp = 0;
        int sub = 0;
        while(!b.isEmpty()){
            int sub1 = a.remove(a.size() - 1) - sub;
            int sub2 = b.remove(b.size() - 1);
            if(sub1 >= sub2){
                tmp = sub1 - sub2;
                sub = 0;
            }else{
                tmp = sub1 + 10 - sub2;
                sub = 1;
            }
            sb.append(tmp);
        }
        while(!a.isEmpty()){
            int su = a.remove(a.size() - 1) - sub;
            if(su < 0){
                su = su + 10;
                sub = 1;
            }else{
                sub = 0;
            }
            sb.append(su);
        }
        while(sb.length() > 0 && sb.charAt(sb.length() - 1) == '0'){
            sb.deleteCharAt(sb.length() - 1);
        }
        if(sb.length() == 0) return "0";
        return sb.reverse().toString();
    }
}