std::ranges::make_heap(3)

✨ std::ranges::make_heap ✨

okay so bestie, this is the C++ Standard Libary manual page for std::ranges::make_heap (section (3), iykyk 💅). It's giving algorithm-girlie energy and honestly? iconic.

💖 NAME 💖

std::ranges::make_heap — std::ranges::make_heap

That's the name section. She's brief, she's self-referential, we love her. 😭

📦 Synopsis 📦

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>
(1) (since C++20)
constexpr I
    make_heap( I first, S last, Comp comp = {}, Proj proj = {} );
template< ranges::random_access_range R, class Comp = ranges::less,
          class Proj = std::identity >
(2) (since C++20)
requires std::sortable<ranges::iterator_t<R>, Comp, Proj>
constexpr ranges::borrowed_iterator_t<R>
    make_heap( R&& r, Comp comp = {}, Proj proj = {} );

It constructs a max heap in the range [first, last). No cap. ✨

1. Elements are compared using the given binary comparison function comp and projection object proj.
2. Same as (1), but uses r as the range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are 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.

In practice, they may be implemented as function objects, or with special compiler extensions.

🦋 Parameters 🦋

• first, last — the range of elements to make the heap from
• r — the range of elements to make the heap from
• pred — predicate to apply to the projected elements
• proj — projection to apply to the elements

🎀 Return value 🎀

An iterator equal to last. That's the whole tea. 💖

⭐ Complexity ⭐

Given N = ranges::distance(first, last), at most 3*N comparisons and 6*N projections. She's doing the math, bestie. ✨

🌸 Notes 🌸

A max heap is a range of elements [f, l), arranged with respect to comparator comp and projection proj, that has the following properties:

• With N = l - f, p = f[(i - 1) / 2], and q = f[i], for all 0 < i < N, the expression std::invoke(comp, std::invoke(proj, p), std::invoke(proj, q)) evaluates to false.
• A new element can be added using ranges::push_heap, in 𝓞(log N) time.
• The first element can be removed using ranges::pop_heap, in 𝓞(log N) time.

🧚 Example 🧚

Run this code, bestie 👇

// Run this code

#include <algorithm>
#include <cmath>
#include <functional>
#include <iostream>
#include <vector>

void out(const auto& what, int n = 1)
{
    while (n-- > 0)
        std::cout << what;
}

void print(auto rem, auto const& v)
{
    out(rem);
    for (auto e : v)
        out(e), out(' ');
    out('\n');
}

void draw_heap(auto const& v)
{
    auto bails = [](int n, int w)
    {
        auto b = [](int w) { out("┌"), out("─", w), out("┴"), out("─", w), out("┐"); };
        if (!(n /= 2))
            return;
        for (out(' ', w); n-- > 0;)
            b(w), out(' ', w + w + 1);
        out('\n');
    };

    auto data = [](int n, int w, auto& first, auto last)
    {
        for (out(' ', w); n-- > 0 && first != last; ++first)
            out(*first), out(' ', w + w + 1);
        out('\n');
    };

    auto tier = [&](int t, int m, auto& first, auto last)
    {
        const int n{1 << t};
        const int w{(1 << (m - t - 1)) - 1};
        bails(n, w), data(n, w, first, last);
    };

    const int m{static_cast<int>(std::ceil(std::log2(1 + v.size())))};
    auto first{v.cbegin()};
    for (int i{}; i != m; ++i)
        tier(i, m, first, v.cend());
}

int main()
{
    std::vector h{1, 6, 1, 8, 0, 3, 3, 9, 8, 8, 7, 4, 9, 8, 9};
    print("source: ", h);

    std::ranges::make_heap(h);
    print("\n" "max-heap: ", h);
    draw_heap(h);

    std::ranges::make_heap(h, std::greater{});
    print("\n" "min-heap: ", h);
    draw_heap(h);
}

🍓 Output 🍓

source: 1 6 1 8 0 3 3 9 8 8 7 4 9 8 9

max-heap: 9 8 9 8 8 4 9 6 1 0 7 1 3 8 3
       9
   ┌───┴───┐
   8       9
 ┌─┴─┐   ┌─┴─┐
 8   8   4   9
┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐
6 1 0 7 1 3 8 3

min-heap: 0 1 1 8 6 3 3 9 8 8 7 4 9 8 9
       0
   ┌───┴───┐
   1       1
 ┌─┴─┐   ┌─┴─┐
 8   6   3   3
┌┴┐ ┌┴┐ ┌┴┐ ┌┴┐
9 8 8 7 4 9 8 9

💜 See also 💜

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

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xoxo bestie 💖 source: http://cppreference.com · version/date: 2024.06.10 · page: std::ranges::make_heap(3) — that's the footer, love u, bye 🫶