组合数取模

 

const int N =1e5+4;
 int fac[N] ,fm[N];
    
inline int kpow(int a, int b) {
	int res = 1;
	for (; b; b >>= 1) {
		if (b & 1)
			res = res * a % mod;
		a = a * a % mod;
	}
	return res;
}

 void getInv() {
	fac[0]= fm[0] = 1;
	for (int i = 1; i <= 10000; ++i) {
		fac[i] = fac[i - 1] * i % mod;
		fm[i] = kpow(fac[i], mod - 2);
	}
}
 inline int C(int n, int m) {
	if (n < 0 || m < 0 || n < m) return 0;
	return fac[n] * fm[m] % mod * fm[n - m] % mod;
}