quicksort.detail.h

// Copyright (c) 2013 Craig Henderson
// https://github.com/cdmh/sorting_algorithms

#pragma once

namespace cdmh {

namespace detail {

template<typename T>
inline T median(T const &t1, T const &t2, T const &t3)
{
    if (t1 < t2)
    {
        if (t2 < t3)
            return t2;
        else if (t1 < t3)
            return t3;
        else
            return t1;
    }
    else if (t1 < t3)
        return t1;
    else if (t2 < t3)
        return t3;
    else
        return t2;
}

template<typename It, typename Pred>
inline std::pair<It,It> quicksort_splits(It begin, It end, Pred pred)
{
    using value_t = typename std::iterator_traits<It>::value_type;
    using namespace std::placeholders;

    auto const not_pred = [&pred](value_t const &first, value_t const &second) { return !pred(second, first); };
    auto const pivot    = detail::median(*begin, *detail::advance(begin, std::distance(begin, end) / 2), *detail::advance(end, -1));
    auto const split    = std::partition(begin, end, std::bind(pred, _1, pivot));
    return std::make_pair(split, std::partition(split, end, std::bind(not_pred, _1, pivot)));
}

}   // namespace detail

}   // namespace cdmh

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