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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[floor( i-1 2 )] does not compare less than f[i].
a new element can be added using std::push_heap()
the first element can be removed using std::pop_heap()

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

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); }

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

#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