# std::ranges::sort_heap

From cppreference.com
< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
template< std::random_access_iterator I, std::sentinel_for <I> S, class Comp = ranges::less, class Proj = std::identity > requires std::sortable <I, Comp, Proj> constexpr I sort_heap( I first, S last, Comp comp = {}, Proj proj = {} ); | (1) | (since C++20)
template< ranges::random_access_range R, class Comp = ranges::less, class Proj = std::identity > requires std::sortable < ranges::iterator_t <R>, Comp, Proj> constexpr ranges::borrowed_iterator_t <R> sort_heap( R&& r, Comp comp = {}, Proj proj = {} ); | (2) | (since C++20)

Sorts the elements in the specified range with respect to comp and proj, where the range originally represents a heap with respect to comp and proj. The sorted range no longer maintains the heap property.

1) The specified range is `[`first`,` last`)`.
2) The specified range is r.

If the specified range is not a heap with respect to comp and proj, the behavior is undefined.

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.

### Parameters

first, last | - | the iterator and sentinel designating the range of elements to modify
r | - | the range of elements to modify
comp | - | comparator to apply to the projected elements
proj | - | projection to apply to the elements

### Return value

1) last
2) ranges::end (r)

### Complexity

At most \(\scriptsize 2N \cdot \log(N)\)2N⋅log(N) applications of comp and \(\scriptsize 4N \cdot \log(N)\)4N⋅log(N) applications of proj, where \(\scriptsize N \)N is:

1) ranges::distance (first, last)
2) ranges::distance (r)

### Possible implementation

    struct sort_heap_fn
    {
        template<std::random_access_iterator I, std::sentinel_for<I> S,
                 class Comp = ranges::less, class Proj = std::identity>
            requires std::sortable<I, Comp, Proj>
        constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
        {
            auto ret{ranges::next(first, last)};
            for (; first != last; --last)
                ranges::pop_heap(first, last, comp, proj);
            return ret;
        }

        template<ranges::random_access_range R,
                 class Comp = ranges::less, class Proj = std::identity>
            requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
        constexpr ranges::borrowed_iterator_t<R>
            operator()(R&& r, Comp comp = {}, Proj proj = {}) const
        {
            return (*this)(ranges::begin(r), ranges::end(r), std::move(comp), std::move(proj));
        }
    };

    inline constexpr sort_heap_fn sort_heap{};

### Example

Run this code

    #include <algorithm>
    #include <array>
    #include <iostream>

    void print(auto const& rem, const auto& v)
    {
        std::cout << rem;
        for (const auto i : v)
            std::cout << i << ' ';
        std::cout << '\n';
    }

    int main()
    {
        std::array v{3, 1, 4, 1, 5, 9};
        print("original array:  ", v);

        std::ranges::make_heap(v);
        print("after make_heap: ", v);

        std::ranges::sort_heap(v);
        print("after sort_heap: ", v);
    }

Output:

    original array:  3 1 4 1 5 9
    after make_heap: 9 5 4 1 1 3
    after sort_heap: 1 1 3 4 5 9

### See also

ranges::is_heap (C++20) | checks if the given range is a max heap (algorithm function object)
ranges::is_heap_until (C++20) | finds the largest subrange that is a max heap (algorithm function object)
ranges::make_heap (C++20) | creates a max heap out of a range of elements (algorithm function object)
ranges::pop_heap (C++20) | removes the largest element from a max heap (algorithm function object)
ranges::push_heap (C++20) | adds an element to a max heap (algorithm function object)
sort_heap | turns a max heap into a range of elements sorted in ascending order (function template)

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