原理:a=kp , b=mp ,p是a和b的公因数;
a-b=(k-m)p ,
则a-b 和min(a,b)的公因数也是p;
r 为a/b的余数 r=(k-nm)*p,
r 和min(a,b)的公因数也是p.
int gcd(int a,int b)
{
int r;
if(a<b)
{
int temp;
temp = a;
a = b;
b = temp;
}
while(1)
{
r = a%b;
if(r==0) break;
else
{
a=b;b=r;
}
}
return b;
}