一次性AC，用时15分钟。

#include<iostream>
using namespace std;
int gcd(int a,int b)
{
    int x=a,y=b,z=-1;
    while(x%y!=0)
    {
        z=x%y;
        x=y;
        y=z;
    }
    return y;
}
int main()
{
//  freopen("xxx.in","r",stdin);
//  freopen("yyy.out","w",stdout);
    int a,b;
    cin >> a >> b;
    cout << gcd(a,b);   
//  fclose(stdin);
//  fclose(stdout);
    return 0;
 }