comparators.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
 *                                                                           *
 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
 *                                                                           *
 * All rights reserved.                                                      *
 *                                                                           *
 * This program is free software; you can redistribute it and/or modify      *
 * it under the terms of the Mozilla Public License Version 2.0 as published *
 * by the Mozilla Foundation; either version 2 of the License, or            *
 * (at your option) any later version.                                       *
 *                                                                           *
 * This program is distributed in the hope that it will be useful,           *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of            *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the              *
 * Mozilla Public License Version 2.0                                        *
 * (https://www.mozilla.org/en-US/MPL/2.0/) for more details.                *
 ****************************************************************************/
 
#ifndef VCL_MISC_COMPARATORS_H
#define VCL_MISC_COMPARATORS_H
 
#include <algorithm>
#include <utility>
 
namespace vcl {
 
template<typename Pair>
struct PairComparator
{
    bool operator()(const Pair& p1, const Pair& p2) const
    {
        if (p1.first == p2.first) {
            return p1.second < p2.second;
        }
        return p1.first < p2.first;
    }
};
 
template<typename T>
struct UnorderedPairComparator
{
    bool operator()(const std::pair<T, T>& p1, const std::pair<T, T>& p2) const
    {
        if (std::min(p1.first, p1.second) < std::min(p2.first, p2.second)) {
            return true;
        }
        else if (
            std::min(p1.first, p1.second) == std::min(p2.first, p2.second)) {
            return std::max(p1.first, p1.second) <
                   std::max(p2.first, p2.second);
        }
        else {
            return false;
        }
    }
};
 
template<typename Pair>
struct FirstElementPairComparator
{
    bool operator()(const Pair& p1, const Pair& p2) const
    {
        return p1.first < p2.first;
    }
};
 
} // namespace vcl
 
#endif // VCL_MISC_COMPARATORS_H