擴展歐幾里得

struct	eu
{
	int a,b,x,y,q;
	void extend_euclid(int a,int b)
	{
		if(b==0)
		{
			x=1;y=0;q=a;
		}
		else
		{
			extend_euclid(b,a%b);
			int tmp=x;
			x=y;y=tmp-a/b*y;
		}
	}
};