mod/floor_monoid_product.hpp

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• Last update: 2024-01-23 03:59:43+09:00
• Include: #include "mod/floor_monoid_product.hpp"
• Link: https://qoj.ac/contest/1411/problem/7620
• Link: https://yukicoder.me/submissions/883884

Depends on

• alg/monoid_pow.hpp

Required by

• mod/floor_sum_of_linear_polynomial.hpp

Verified with

• test/library_checker/math/sum_of_floor_of_linear_2.test.cpp
• test/mytest/floor_sum_of_polynomial.test.cpp
• test/yukicoder/2362.test.cpp

Code

#include "alg/monoid_pow.hpp"

// https://yukicoder.me/submissions/883884
// https://qoj.ac/contest/1411/problem/7620
// U は範囲内で ax+b がオーバーフローしない程度
// yyy x yyyy x ... yyy x yyy (x を N 個)
// k 個目の x までに floor(ak+b,m) 個の y がある
// my<=ax+b における lattice path における辺の列と見なせる
template <typename Monoid, typename X, typename U>
X floor_monoid_product(X x, X y, U N, U a, U b, U m) {
  U c = (a * N + b) / m;
  X pre = Monoid::unit(), suf = Monoid::unit();
  while (1) {
    const U p = a / m, q = b / m;
    a %= m, b %= m;
    x = Monoid::op(x, monoid_pow<Monoid>(y, p));
    pre = Monoid::op(pre, monoid_pow<Monoid>(y, q));
    c -= (p * N + q);
    if (c == 0) break;
    const U d = (m * c - b - 1) / a + 1;
    suf = Monoid::op(y, Monoid::op(monoid_pow<Monoid>(x, N - d), suf));
    b = m - b - 1 + a, N = c - 1, c = d;
    swap(m, a), swap(x, y);
  }
  x = monoid_pow<Monoid>(x, N);
  return Monoid::op(Monoid::op(pre, x), suf);
}

#line 2 "alg/monoid_pow.hpp"

// chat gpt
template <typename U, typename Arg1, typename Arg2>
struct has_power_method {
private:
  // ヘルパー関数の実装
  template <typename V, typename A1, typename A2>
  static auto check(int)
      -> decltype(std::declval<V>().power(std::declval<A1>(),
                                          std::declval<A2>()),
                  std::true_type{});
  template <typename, typename, typename>
  static auto check(...) -> std::false_type;

public:
  // メソッドの有無を表す型
  static constexpr bool value = decltype(check<U, Arg1, Arg2>(0))::value;
};

template <typename Monoid>
typename Monoid::X monoid_pow(typename Monoid::X x, ll exp) {
  using X = typename Monoid::X;
  if constexpr (has_power_method<Monoid, X, ll>::value) {
    return Monoid::power(x, exp);
  } else {
    assert(exp >= 0);
    X res = Monoid::unit();
    while (exp) {
      if (exp & 1) res = Monoid::op(res, x);
      x = Monoid::op(x, x);
      exp >>= 1;
    }
    return res;
  }
}
#line 2 "mod/floor_monoid_product.hpp"

// https://yukicoder.me/submissions/883884
// https://qoj.ac/contest/1411/problem/7620
// U は範囲内で ax+b がオーバーフローしない程度
// yyy x yyyy x ... yyy x yyy (x を N 個)
// k 個目の x までに floor(ak+b,m) 個の y がある
// my<=ax+b における lattice path における辺の列と見なせる
template <typename Monoid, typename X, typename U>
X floor_monoid_product(X x, X y, U N, U a, U b, U m) {
  U c = (a * N + b) / m;
  X pre = Monoid::unit(), suf = Monoid::unit();
  while (1) {
    const U p = a / m, q = b / m;
    a %= m, b %= m;
    x = Monoid::op(x, monoid_pow<Monoid>(y, p));
    pre = Monoid::op(pre, monoid_pow<Monoid>(y, q));
    c -= (p * N + q);
    if (c == 0) break;
    const U d = (m * c - b - 1) / a + 1;
    suf = Monoid::op(y, Monoid::op(monoid_pow<Monoid>(x, N - d), suf));
    b = m - b - 1 + a, N = c - 1, c = d;
    swap(m, a), swap(x, y);
  }
  x = monoid_pow<Monoid>(x, N);
  return Monoid::op(Monoid::op(pre, x), suf);
}

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