Maybe monoid
(Mylib/AlgebraicStructure/Monoid/maybe.cpp)

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• Last update: 2021-04-23 23:44:44+09:00
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Notes

Problems

References

Verified with

• test/yukicoder/1030/main.test.cpp

Code

#pragma once
#include <optional>

namespace haar_lib {
  template <typename Semigroup>
  struct maybe_monoid {
    using value_type = std::optional<typename Semigroup::value_type>;
    const static Semigroup S;

    value_type operator()() const { return std::nullopt; }
    value_type operator()(const value_type &a, const value_type &b) const {
      if (not a) return b;
      if (not b) return a;
      return {S(*a, *b)};
    }
  };
}  // namespace haar_lib

#line 2 "Mylib/AlgebraicStructure/Monoid/maybe.cpp"
#include <optional>

namespace haar_lib {
  template <typename Semigroup>
  struct maybe_monoid {
    using value_type = std::optional<typename Semigroup::value_type>;
    const static Semigroup S;

    value_type operator()() const { return std::nullopt; }
    value_type operator()(const value_type &a, const value_type &b) const {
      if (not a) return b;
      if (not b) return a;
      return {S(*a, *b)};
    }
  };
}  // namespace haar_lib

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