组合数板子

组合数板子

using i64 = int64_t;
constexpr i64 mod = 1e9 + 7;
i64 fpow(i64 x, i64 r)
{
    i64 result = 1;
    while (r)
    {
        if (r & 1)result = result * x % mod;
        r >>= 1;
        x = x * x % mod;
    }
    return result;
}

namespace binom {
    i64 fac[N], ifac[N];
    int __ = []
    {
        fac[0] = 1;
        for (int i = 1; i <= N - 5; i++)
            fac[i] = fac[i - 1] * i % mod;
        ifac[N - 5] = fpow(fac[N - 5], mod - 2);
        for (int i = N - 5; i; i--)
            ifac[i - 1] = ifac[i] * i % mod;
        return 0;
    }();

    inline i64 C(int n, int m)
    {
        if (n < m || m < 0)return 0;
        return fac[n] * ifac[m] % mod * ifac[n - m] % mod;
    }

    inline i64 A(int n, int m)
    {
        if (n < m || m < 0)return 0;
        return fac[n] * ifac[n - m] % mod;
    }
}
using namespace binom;

比较快的板子 我也是从别人那学来的板子（bushi