运行结果与下载的测试点4.out文件一模一样，为什么过不了呢

#include <iostream>
#include <cstring>
using namespace std;
string a,b;
int flag[10001];
int main(){
	cin>>b>>a;
	for(int i = 0;i<a.length();i++){
		flag[i] = a[i]>='a'?1:0;
		a[i]-=(a[i]<='Z'?'A':'a');
		b[i]-=(b[i]<='Z'?'A':'a');
	}
	for(int i = 0,j = 0;i<a.length();i++,j++){
		j = j>=b.length()?0:j;
		cout<<char((a[i]-b[j]<0?a[i]+26:a[i])-b[j]+(flag[i]?'a':'A'));
	}
	return 0;
}