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std::ranges::pop_heap

Defined in header <algorithm>

Call signature

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 pop_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> pop_heap( R&& r, Comp comp = {}, Proj proj = {} );	(2)	(since C++20)

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
    pop_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>
    pop_heap( R&& r, Comp comp = {}, Proj proj = {} );

(2)

(since C++20)

Swaps the value in the position first and the value in the position last - 1 and makes the subrange [first, last - 1) into a max heap. This has the effect of removing the first element from the heap defined by the range [first, last).

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 defining the valid nonempty heap to modify
r	-	the range of elements defining the valid nonempty heap to modify
pred	-	predicate to apply to the projected elements
proj	-	projection to apply to the elements

Return value

An iterator equal to last.

Complexity

Given N = ranges::distance(first, last), at most \(\scriptsize 2\log{(N)}\)2log(N) comparisons and \(\scriptsize 4\log{(N)}\)4log(N) projections.

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 \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.
The first element can be removed using ranges::pop_heap, in \(\scriptsize \mathcal{O}(\log N)\)𝓞(log N) time.

Example

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <string_view>
 
template<class I = int*>
void print(std::string_view rem, I first = {}, I last = {},
           std::string_view term = "\n")
{
    for (std::cout << rem; first != last; ++first)
        std::cout << *first << ' ';
    std::cout << term;
}
 
int main()
{
    std::array v {3, 1, 4, 1, 5, 9, 2, 6, 5, 3};
    print("initially, v: ", v.cbegin(), v.cend());
 
    std::ranges::make_heap(v);
    print("make_heap, v: ", v.cbegin(), v.cend());
 
    print("convert heap into sorted array:");
    for (auto n {std::ssize(v)}; n >= 0; --n)
    {
        std::ranges::pop_heap(v.begin(), v.begin() + n);
        print("[ ", v.cbegin(), v.cbegin() + n, "]  ");
        print("[ ", v.cbegin() + n, v.cend(), "]\n");
    }
}

Output:

initially, v: 3 1 4 1 5 9 2 6 5 3
make_heap, v: 9 6 4 5 5 3 2 1 1 3
convert heap into sorted array:
[ 6 5 4 3 5 3 2 1 1 9 ]  [ ]
[ 5 5 4 3 1 3 2 1 6 ]  [ 9 ]
[ 5 3 4 1 1 3 2 5 ]  [ 6 9 ]
[ 4 3 3 1 1 2 5 ]  [ 5 6 9 ]
[ 3 2 3 1 1 4 ]  [ 5 5 6 9 ]
[ 3 2 1 1 3 ]  [ 4 5 5 6 9 ]
[ 2 1 1 3 ]  [ 3 4 5 5 6 9 ]
[ 1 1 2 ]  [ 3 3 4 5 5 6 9 ]
[ 1 1 ]  [ 2 3 3 4 5 5 6 9 ]
[ 1 ]  [ 1 2 3 3 4 5 5 6 9 ]
[ ]  [ 1 1 2 3 3 4 5 5 6 9 ]