大数公约数
#include <iostream>
#include <string>
using namespace std;
string s;
long long gcd(long long a, long long b)
{
if (a % b == 0)
return b;
else
return gcd(b, a % b);
}
int main()
{
cin >> s;
long long b; cin >> b;
long long a = 0;//范围问题，借助字符串
for (int i = 0; s[i] != '\0'; i++)
a = (a * 10 + s[i] - '0') % b;//保证了一定比b小，long long不会溢出
cout << gcd(a, b);
system("pause");
return 0;
} 
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