libcruft-util/algo/search.hpp

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/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright:
* 2018, Danny Robson <danny@nerdcruft.net>
*/
#pragma once
#include "../types/traits.hpp"
#include <iterator>
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#include <functional>
namespace cruft::search {
/// Performs a linear search to discover the iterator corresponding to
/// the value which minimises a function.
///
/// Useful as a mechanism to avoid possibly expensive comparison
/// calculations; eg recomputing path distances when testing a series of
/// possible routes.
///
/// The provided function will be invoked with the supplied argument pack
/// as the first arguments and the dereferenced iterator as the final
/// argument.
///
/// \tparam ForwardT A forward iterator
/// \tparam FunctionT An invokable
/// \param first The first iterator in the range to be searched
/// \param last The last iterator in the range to be searched
/// \param func A functional which returns a comparable value
/// \param args The first arguments passed to `func`
/// \return A pair of the best score, and the best iterator
template <
typename ForwardT,
typename FunctionT,
typename ...Args
>
auto
minimises (
ForwardT first,
ForwardT last,
FunctionT &&func,
Args &&...args
) {
using value_type = typename std::iterator_traits<ForwardT>::value_type;
using score_t = std::invoke_result_t<FunctionT, Args..., value_type>;
static_assert (::cruft::is_orderable_v<score_t>);
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auto best_score = std::invoke (func, args..., *first);
auto best_item = first;
for (++first; first != last; ++first) {
auto this_score = std::invoke (func, args..., *first);
if (this_score < best_score) {
best_score = this_score;
best_item = first;
}
}
return std::pair (std::move (best_score), std::move (best_item));
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}
}