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std::ranges::minmax_element, std::ranges::minmax_element_result - cppreference.com

Call signature

Helper types

1) Finds the smallest and largest elements in the range [first, last).

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

An object consisting of an iterator to the smallest element as the first element and an iterator to the greatest element as the second. Returns {first, first} if the range is empty. If several elements are equivalent to the smallest element, the iterator to the first such element is returned. If several elements are equivalent to the largest element, the iterator to the last such element is returned.

At most std::max(std::floor(1.5 * (N − 1)), 0.0) applications of the comparison and twice as many applications of the projection, where N = ranges::distance(first, last).

struct minmax_element_fn
{
    template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
             std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
    constexpr ranges::minmax_element_result<I>
        operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
    {
        auto min = first, max = first;
 
        if (first == last || ++first == last)
            return {min, max};
 
        if (std::invoke(comp, std::invoke(proj, *first),
                              std::invoke(proj, *min)))
            min = first;
        else
            max = first;
 
        while (++first != last)
        {
            auto i = first;
            if (++first == last)
            {
                if (std::invoke(comp, std::invoke(proj, *i),
                                      std::invoke(proj, *min)))
                    min = i;
                else if (!(std::invoke(comp, std::invoke(proj, *i),
                                             std::invoke(proj, *max))))
                    max = i;
                break;
            }
            else
            {
                if (std::invoke(comp, std::invoke(proj, *first),
                                      std::invoke(proj, *i)))
                {
                  if (std::invoke(comp, std::invoke(proj, *first),
                                        std::invoke(proj, *min)))
                      min = first;
                  if (!(std::invoke(comp, std::invoke(proj, *i),
                                          std::invoke(proj, *max))))
                      max = i;
                }
                else
                {
                    if (std::invoke(comp, std::invoke(proj, *i),
                                          std::invoke(proj, *min)))
                        min = i;
                    if (!(std::invoke(comp, std::invoke(proj, *first),
                                            std::invoke(proj, *max))))
                        max = first;
                }
            }
        }
        return {min, max};
    }
 
    template<ranges::forward_range R, class Proj = std::identity,
             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
    constexpr ranges::minmax_element_result<ranges::borrowed_iterator_t<R>>
        operator()(R&& r, Comp comp = {}, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
    }
};
 
inline constexpr minmax_element_fn minmax_element;

#include <algorithm>
#include <iostream>
#include <iterator>
namespace ranges = std::ranges;
 
int main()
{
    const auto v = {3, 9, 1, 4, 1, 2, 5, 9};
    const auto [min, max] = ranges::minmax_element(v);
    std::cout
        << "min = " << *min << ", at [" << ranges::distance(v.begin(), min) << "]\n"
        << "max = " << *max << ", at [" << ranges::distance(v.begin(), max) << "]\n";
}

Output:

min = 1, at [2]
max = 9, at [7]

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