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std::ranges::pop_heap(3)       C++ Standard Libary	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 ef-
     fect 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  inhib-
     ited.

	In  practice,  they may be implemented as function objects, or with spe-
     cial 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 com-
     parator 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 \(\scriptsize
	    \mathcal{O}(\log N)\)dh(log N) time.
	  *  The  first  element  can  be  removed  using  ranges::pop_heap,  in
     \(\scriptsize
	    \mathcal{O}(\log N)\)dh(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)

http://cppreference.com 	   2024.06.10		std::ranges::pop_heap(3)
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