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std::ranges::pop_heap

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
ranges::pop_heap
Minimum/maximum operations
Permutations
 
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

ranges::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>

ranges::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:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] 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.

[edit] Return value

An iterator equal to last.

[edit] Complexity

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

[edit] Notes

The 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, for all 0 < i < N, p = f[floor(
    i-1
    2
    )], and q = f[i], 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 𝓞(log N) time.
  • the first element can be removed using ranges::pop_heap(), in 𝓞(log N) time.

[edit] 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 ]

[edit] See also

adds an element to a max heap
(niebloid) [edit]
checks if the given range is a max heap
(niebloid) [edit]
finds the largest subrange that is a max heap
(niebloid) [edit]
creates a max heap out of a range of elements
(niebloid) [edit]
turns a max heap into a range of elements sorted in ascending order
(niebloid) [edit]
removes the largest element from a max heap
(function template) [edit]