NAME¶

std::ranges::pop_heap - std::ranges::pop_heap

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

pop_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>

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

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¶

// Run this code

#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 ]

See also¶

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