欧几里得算法

int gcd(int a,int b)
{
	if(b==0)
		return a;
	return gcd(b,a%b);
}
int gcd(int a,int b)
{
	return b==0?a:gcd(b,a%b);
}
int gcd(int a,int b)
{
	while(b!=0)
	{
		int r=b;
		b=a%b;
		a=r;
	}
	return a;
}

参考http://www.cnblogs.com/frog112111/archive/2012/08/19/2646012.html