扩展欧几里德模版

参考资料：Arimura          |       kasumi

int gcd(int a, int b){
	return b==0?a:gcd(b, a%b);
}
void exgcd(int a, int b, int &x, int &y){
	if(b==0){
		x = 1;
		y = 0;
		return;
	}
	exgcd(b, a%b, x, y);
	int tmp = x;
	x = y;
	y = tmp-a/b*y;
}