eq_by_less.hpp

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// -*- C++ -*-

// Copyright (C) 2005-2019 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
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// version.

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// Under Section 7 of GPL version 3, you are granted additional
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// 3.1, as published by the Free Software Foundation.

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// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.

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/**
 * @file eq_by_less.hpp
 * Contains an equivalence function.
 */

#ifndef PB_DS_EQ_BY_LESS_HPP
#define PB_DS_EQ_BY_LESS_HPP

#include <utility>
#include <functional>
#include <vector>
#include <assert.h>
#include <ext/pb_ds/detail/types_traits.hpp>

namespace __gnu_pbds
{
  namespace detail
  {
    /// Equivalence function.
    template<typename Key, class Cmp_Fn>
    struct eq_by_less : private Cmp_Fn
    {
      bool
      operator()(const Key& r_lhs, const Key& r_rhs) const
      {
        const bool l = Cmp_Fn::operator()(r_lhs, r_rhs);
        const bool g = Cmp_Fn::operator()(r_rhs, r_lhs);
        return !(l || g);
      }
    };
  } // namespace detail
} // namespace __gnu_pbds

#endif // #ifndef PB_DS_EQ_BY_LESS_HPP