求C(n, m) % mod
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#include <bits/stdc++.h>using namespace std;long long fact[200200];long long inv[200200];const int mod = 1e9 + 7;long long qpow(long long x, long long n){ long long ans = 1; while (n) { if (n & 1) ans = ans * x % mod; x = x * x % mod; n >>= 1; } return ans;}void init(){ fact[0] = 1; for (int i = 1; i < 200005; i++) fact[i] = fact[i - 1] * i % mod; for (int i = 0; i < 200005; i++) inv[i] = qpow(fact[i], mod - 2);}long long C(int n, int m){ return fact[n] * inv[n - m] % mod * inv[m] % mod;}int main(){ init(); int n, m; while(cin >> n >> m) { cout << C(n, m) << endl; }} |