std::sort_heap

Defined in header `<algorithm>`
	(1)
template< class RandomIt > void sort_heap( RandomIt first, RandomIt last );			(until C++20)
template< class RandomIt > constexpr void sort_heap( RandomIt first, RandomIt last );			(since C++20)
		(2)
template< class RandomIt, class Compare > void sort_heap( RandomIt first, RandomIt last, Compare comp );				(until C++20)
template< class RandomIt, class Compare > constexpr void sort_heap( RandomIt first, RandomIt last, Compare comp );				(since C++20)

Converts the max heap [first, last) into a sorted range in ascending order. The resulting range no longer has the heap property.

The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements to sort
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 ValueSwappable and LegacyRandomAccessIterator.
- The type of dereferenced `RandomIt` must meet the requirements of MoveAssignable and MoveConstructible.

Return value

(none)

Complexity

At most 2×N×log(N) comparisons where N=std::distance(first, last).

Notes

A max heap is a range of elements [f,l) that has the following properties:

With N = l-f, for all 0 < i < N, f[(i-1)/2] does not compare less than f[i].
A new element can be added using std::push_heap, in $\scriptsize \mathcal{O}(\log N)$ $𝓞(log N)$ time.
The first element can be removed using std::pop_heap, in $\scriptsize \mathcal{O}(\log N)$ $𝓞(log N)$ time.

Possible implementation

First version

template< class RandomIt >
void sort_heap( RandomIt first, RandomIt last )
{
    while (first != last)
        std::pop_heap(first, last--);
}

Second version

template< class RandomIt, class Compare >
void sort_heap( RandomIt first, RandomIt last, Compare comp )
{
    while (first != last)
        std::pop_heap(first, last--, comp);
}

Example

Run this code

#include <algorithm>
#include <vector>
#include <iostream>
 
int main()
{
    std::vector<int> v = {3, 1, 4, 1, 5, 9}; 
 
    std::make_heap(v.begin(), v.end());
 
    std::cout << "heap:\t";
    for (const auto &i : v) {
        std::cout << i << ' ';
    }   
 
    std::sort_heap(v.begin(), v.end());
 
    std::cout << "\nsorted:\t";
    for (const auto &i : v) {                                                   
        std::cout << i << ' ';
    }   
    std::cout << '\n';
}

Output:

heap:   9 4 5 1 1 3 
sorted: 1 1 3 4 5 9

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 2444	C++98	complexity requirement was wrong by a factor of 2	corrected

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

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)
push_heap	adds an element to a max heap (function template)
ranges::sort_heap (C++20)	turns a max heap into a range of elements sorted in ascending order (niebloid)