Mod-Int

説明

mod M での四則演算を行う構造体である。

計算量

• 加減乗算 $O(1)$
• 除算 $O(\log N)$ ($M$ は素数)

実装例

template< int mod >
struct ModInt {
  int x;

  ModInt() : x(0) {}

  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}

  ModInt &operator+=(const ModInt &p) {
    if((x += p.x) >= mod) x -= mod;
    return *this;
  }

  ModInt &operator-=(const ModInt &p) {
    if((x += mod - p.x) >= mod) x -= mod;
    return *this;
  }

  ModInt &operator*=(const ModInt &p) {
    x = (int) (1LL * x * p.x % mod);
    return *this;
  }

  ModInt &operator/=(const ModInt &p) {
    *this *= p.inverse();
    return *this;
  }

  ModInt operator-() const { return ModInt(-x); }

  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }

  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }

  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }

  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }

  bool operator==(const ModInt &p) const { return x == p.x; }

  bool operator!=(const ModInt &p) const { return x != p.x; }

  ModInt inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while(b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }

  ModInt pow(int64_t n) const {
    ModInt ret(1), mul(x);
    while(n > 0) {
      if(n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  friend ostream &operator<<(ostream &os, const ModInt &p) {
    return os << p.x;
  }

  friend istream &operator>>(istream &is, ModInt &a) {
    int64_t t;
    is >> t;
    a = ModInt< mod >(t);
    return (is);
  }

  static int get_mod() { return mod; }
};

using modint = ModInt< mod >;

任意Mod-Int

その型を使う前に ArbitraryModInt::set_mod($md$) をすること.

struct ArbitraryModInt {

  int x;

  ArbitraryModInt() : x(0) {}

  ArbitraryModInt(int64_t y) : x(y >= 0 ? y % mod() : (mod() - (-y) % mod()) % mod()) {}

  static int &mod() {
    static int mod = 0;
    return mod;
  }

  static int set_mod(int md) {
    mod() = md;
  }

  ArbitraryModInt &operator+=(const ArbitraryModInt &p) {
    if((x += p.x) >= mod()) x -= mod();
    return *this;
  }

  ArbitraryModInt &operator-=(const ArbitraryModInt &p) {
    if((x += mod() - p.x) >= mod()) x -= mod();
    return *this;
  }

  ArbitraryModInt &operator*=(const ArbitraryModInt &p) {
    unsigned long long a = (unsigned long long) x * p.x;
    unsigned xh = (unsigned) (a >> 32), xl = (unsigned) a, d, m;
    asm("divl %4; \n\t" : "=a" (d), "=d" (m) : "d" (xh), "a" (xl), "r" (mod()));
    x = m;
    return *this;
  }

  ArbitraryModInt &operator/=(const ArbitraryModInt &p) {
    *this *= p.inverse();
    return *this;
  }

  ArbitraryModInt operator-() const { return ArbitraryModInt(-x); }

  ArbitraryModInt operator+(const ArbitraryModInt &p) const { return ArbitraryModInt(*this) += p; }

  ArbitraryModInt operator-(const ArbitraryModInt &p) const { return ArbitraryModInt(*this) -= p; }

  ArbitraryModInt operator*(const ArbitraryModInt &p) const { return ArbitraryModInt(*this) *= p; }

  ArbitraryModInt operator/(const ArbitraryModInt &p) const { return ArbitraryModInt(*this) /= p; }

  bool operator==(const ArbitraryModInt &p) const { return x == p.x; }

  bool operator!=(const ArbitraryModInt &p) const { return x != p.x; }

  ArbitraryModInt inverse() const {
    int a = x, b = mod(), u = 1, v = 0, t;
    while(b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ArbitraryModInt(u);
  }

  ArbitraryModInt pow(int64_t n) const {
    ArbitraryModInt ret(1), mul(x);
    while(n > 0) {
      if(n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  friend ostream &operator<<(ostream &os, const ArbitraryModInt &p) {
    return os << p.x;
  }

  friend istream &operator>>(istream &is, ArbitraryModInt &a) {
    int64_t t;
    is >> t;
    a = ArbitraryModInt(t);
    return (is);
  }
};