一道Lucas定理的板子题
#include<bits/stdc++.h> using namespace std; typedef long long ll; const ll P = 1e9 + 7; const int N = 3e6 + 100; ll fac[N], inv[N]; inline ll C(int n, int m) { if (n < m) return 0; return fac[n] * inv[m] % P * inv[n - m] % P; } inline ll qpow(ll a, ll b, ll p) { ll res = 1; while (b) { if (b & 1) res = res * a % p; a = a * a % p; b >>= 1; } return res; } int main () { int n, m; ios::sync_with_stdio(false); cin >> m >> n; fac[0] = 1; for (int i = 1; i <= 2 * n; ++i) fac[i] = fac[i - 1] * i % P; inv[2 * n] = qpow(fac[2 * n], P - 2, P); for (int i = 2 * n - 1; i >= 0; --i) inv[i] = inv[i + 1] * (i + 1ll) % P; cout << C(n - 1, m - 1) << " " << C(n + m - 1, m - 1) << endl; return 0; }
https://www.cnblogs.com/fzl194/p/9095177.html
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