#include <bits/stdc++.h>
using namespace std;
const long long MOD=1e9+7;
string tru(string a, string b){
int x=0; // Số dư mỗi khi sang hàng khác
int y=0; // Tính số mỗi khi sang hàng khác
string ans="";
a.insert(0,max(0,(int)(b.length()-a.length())),'0'); // Thêm vào ký tự 0 để sao cho xâu a có ký tự bằng b!
b.insert(0,max(0,(int)(a.length()-b.length())),'0');
for (int i=a.length()-1;i>=0;i--){
y=((int)a[i]-38)-((int)b[i]-48)-x; // trừ 48,38 thì tra bảng Ascii sẽ hiểu, tự làm nhé
if(y<10) x=1;
else x=0;
ans=(char)(y%10+48)+ans; //chuyển lại về ký tự để cho xâu
}
while (ans[0]=='0'&&ans.length()>1) ans.erase(0,1); //Để loại bỏ hàng lớn nhất nếu trừ triệt tiêu cho nhau!
return ans;
}
signed main(){
string m="6767676767676767676767676767676767";
string n="3636363636363636363636363636363636";
cout << tru(m,n);
}
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