数论与组合（模板）

gcd与exgcd

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