SP27561 GDCOFTI - Greatest Common Divisor Of Three Integers

#include
using namespace std;
#define ll long long
//#define LOCAL
int main(){
#ifdef LOCAL
    freopen("data.in","r",stdin);
    freopen("data.out","w",stdout);
#endif // LOCAL
    ll a,b,c;
    cin>>a>>b>>c;
    cout<<__gcd(__gcd(a,b),c);
}

C++ 自带__gcd

下面是手写gcd

#define ll long long 
ll gcd(ll a,ll b){
    return !b ? a : gcd(b,a%b);
}