std::ranges::pop_heap(3)

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)