取模+组合数

jiangly的板子

//------取模机------//
using i64 = long long;
template<class T>
constexpr T power(T a, i64 b) {
    T res {1};
    for (; b; b /= 2, a *= a) {
        if (b % 2) {
            res *= a;
        }
    }
    return res;
} // 快速幂

constexpr i64 mul(i64 a, i64 b, i64 p) {
    i64 res = a * b - i64(1.L * a * b / p) * p;
    res %= p;
    if (res < 0) {
        res += p;
    }
    return res;
} // 取模乘

template<i64 P>
struct MInt {
    i64 x;
    constexpr MInt() : x {0} {}
    constexpr MInt(i64 x) : x {norm(x % getMod())} {}

    static i64 Mod;
    constexpr static i64 getMod() {
        if (P > 0) {
            return P;
        } else {
            return Mod;
        }
    }
    constexpr static void setMod(i64 Mod_) {
        Mod = Mod_;
    }//只有P<=0, setMod才生效
    constexpr i64 norm(i64 x) const {
        if (x < 0) {
            x += getMod();
        }
        if (x >= getMod()) {
            x -= getMod();
        }
        return x;
    }
    constexpr i64 val() const {
        return x;
    }
    constexpr MInt operator-() const {
        MInt res;
        res.x = norm(getMod() - x);
        return res;
    }
    constexpr MInt inv() const {
        return power(*this, getMod() - 2);
    }
    constexpr MInt &operator*=(MInt rhs) & {
        if (getMod() < (1ULL << 31)) {
            x = x * rhs.x % int(getMod());
        } else {
            x = mul(x, rhs.x, getMod());
        }
        return *this;
    }
    constexpr MInt &operator+=(MInt rhs) & {
        x = norm(x + rhs.x);
        return *this;
    }
    constexpr MInt &operator-=(MInt rhs) & {
        x = norm(x - rhs.x);
        return *this;
    }
    constexpr MInt &operator/=(MInt rhs) & {
        return *this *= rhs.inv();
    }
    friend constexpr MInt operator*(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res *= rhs;
        return res;
    }
    friend constexpr MInt operator+(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res += rhs;
        return res;
    }
    friend constexpr MInt operator-(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res -= rhs;
        return res;
    }
    friend constexpr MInt operator/(MInt lhs, MInt rhs) {
        MInt res = lhs;
        res /= rhs;
        return res;
    }
    friend constexpr std::istream &operator>>(std::istream &is, MInt &a) {
        i64 v;
        is >> v;
        a = MInt(v);
        return is;
    }
    friend constexpr std::ostream &operator<<(std::ostream &os, const MInt &a) {
        return os << a.val();
    }
    friend constexpr bool operator==(MInt lhs, MInt rhs) {
        return lhs.val() == rhs.val();
    }
    friend constexpr bool operator!=(MInt lhs, MInt rhs) {
        return lhs.val() != rhs.val();
    }
    friend constexpr bool operator<(MInt lhs, MInt rhs) {
        return lhs.val() < rhs.val();
    }
};

template<>
i64 MInt<0>::Mod = 998244353; //只有P<=0, Mod才生效

constexpr int P = 998244353; //在这设置要用的模数
using Z = MInt<P>;
//------取模机------//

//----计算组合数----//
struct Comb {
   int n;
   std::vector<Z> _fac; //阶乘
   std::vector<Z> _invfac; //阶乘的逆元
   std::vector<Z> _inv; //数字的逆元

   Comb() : n{0}, _fac{1}, _invfac{1}, _inv{0} {}
   Comb(int n) : Comb() {
      init(n);
   }

   void init(int m) {
      m = std::min<i64>(m, Z::getMod() - 1);
      if (m <= n) return;
      _fac.resize(m + 1);
      _invfac.resize(m + 1);
      _inv.resize(m + 1);

      for (int i = n + 1; i <= m; i++) {
         _fac[i] = _fac[i - 1] * i;
      }
      _invfac[m] = _fac[m].inv();
      for (int i = m; i > n; i--) {
         _invfac[i - 1] = _invfac[i] * i;
         _inv[i] = _invfac[i] * _fac[i - 1];
      }
      n = m;
   }

   Z fac(int m) {
      if (m > n) init(2 * m);
      return _fac[m];
   }
   Z invfac(int m) {
      if (m > n) init(2 * m);
      return _invfac[m];
   }
   Z inv(int m) {
      if (m > n) init(2 * m);
      return _inv[m];
   }
   Z C(int n, int m) {
      if (n < m || m < 0) return 0;
      return fac(n) * invfac(m) * invfac(n - m);
   }
   Z A(int n, int m) {
      if (n < m || m < 0 ) return 0;
      return fac(n) * invfac(n - m);
   }
} comb;
//----计算组合数----//