std::push_heap(3)

🦋 std::push_heap(3) — C++ Standard Libary bestie briefing 🦋

okay so bestie, this is the std::push_heap(3) page, and we're gonna make heap insertion make sense without losing a single tiny detail. C++ girlies stay winning. 💅

🌸 NAME 🌸

std::push_heap — yep, the original NAME line is literally std::push_heap - std::push_heap. Self-titled icon behavior, periodt.

✨ Synopsis ✨

Defined in header <algorithm>:

template< class RandomIt >                               (1)
(constexpr since C++20)
void push_heap( RandomIt first, RandomIt last );
template< class RandomIt, class Compare >
void push_heap( RandomIt first, RandomIt last, Compare   (2)
(constexpr since C++20)
comp );

It inserts the element at the position last - 1 into the heap [first, last - 1). The heap after the insertion will be [first, last).

1. The heap is with respect to operator< (until C++20) / std::less{} (since C++20).
2. The heap is with respect to comp.

🚨 undefined behavior check, bestie: if any of the following conditions is satisfied, the behavior is undefined:

• [first, last - 1) is not a heap.
• The type of *first is not Swappable. (until C++11)
• RandomIt is not ValueSwappable.
• The type of *first is not MoveConstructible. (since C++11)
• The type of *first is not MoveAssignable.

🎀 Parameters 🎀

• first, last — the range indicating the heap after the insertion.
• comp — comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than the second.

The signature of the comparison function should be equivalent to the following:

bool cmp(const Type1& a, const Type2& b);

While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1& is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them.

🦋 Type requirements 🦋

• RandomIt must meet the requirements of LegacyRandomAccessIterator.
• Compare must meet the requirements of Compare.

🔥 Complexity 🔥

Given N as std::distance(first, last):

1. At most log(N) comparisons using operator< (until C++20) / std::less{} (since C++20).
2. At most log(N) applications of the comparison function comp.

🌈 Example 🌈

// Run this code

#include <algorithm>
#include <iostream>
#include <string_view>
#include <vector>

void println(std::string_view rem, const std::vector<int>& v)
{
    std::cout << rem;
    for (int e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}

int main()
{
    std::vector<int> v{3, 1, 4, 1, 5, 9};

    std::make_heap(v.begin(), v.end());
    println("after make_heap: ", v);

    v.push_back(6);
    println("after push_back: ", v);

    std::push_heap(v.begin(), v.end());
    println("after push_heap: ", v);
}

🎬 Output 🎬

after make_heap: 9 5 4 1 1 3
after push_back: 9 5 4 1 1 3 6
after push_heap: 9 5 6 1 1 3 4

💀 Defect reports 💀

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• LWG 3032, applied to C++98 — as published, the elements of [first, last) was not required to be swappable; correct behavior: required.

💖 See also 💖

• is_heap (C++11) — checks if the given range is a max heap. (function template)
• is_heap_until (C++11) — finds the largest subrange that is a max heap. (function template)
• make_heap — creates a max heap out of a range of elements. (function template)
• pop_heap — removes the largest element from a max heap. (function template)
• sort_heap — turns a max heap into a range of elements sorted in ascending order. (function template)
• ranges::push_heap (C++20) — adds an element to a max heap. (niebloid)

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💖 source/version/date: http://cppreference.com · 2024.06.10 · manual page std::push_heap(3). bestie, go push that heap and slay. 🫶