题解 100% AC

#include <bits/stdc++.h>
using namespace std;
int a[10010],b[10010],c[10010];
int main(){
	string as,bs;
	cin>>as>>bs;
	if(as.size()<bs.size()||as.size()==bs.size()&&as<bs){
		swap(as,bs);
		cout<<"-";
	}
	reverse(as.begin(),as.end()),reverse(bs.begin(),bs.end());
	a[0]=as.size(),b[0]=bs.size(),c[0]=a[0];
	for(int i=0;i<as.length();i++)a[i+1]=as[i]-48;
	for(int i=0;i<bs.length();i++)b[i+1]=bs[i]-48;
	for(int i=1;i<=c[0];i++){
        if(a[i]<b[i]){
        	a[i+1]-=1;
        	a[i]+=10;
		}
		c[i]=a[i]-b[i];
	}
	while(c[c[0]]==0&&c[0]>1)c[0]--;
	for(int i=c[0];i>=1;i--)cout<<c[i];
	return 0;
}