更相减损术
https://baike.baidu.com/item/更相减损术/449183
c++ 代码
#include <iostream>
using namespace std;
int gcd(int a,int b){
while(a != b) {
if (a > b) a-=b;
else b -= a;
}
return a;
}
int main(void) {
int a,b;
cin >> a >> b;
cout << gcd(a,b) << endl;
}