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std::pop_heap(3)	       C++ Standard Libary		std::pop_heap(3)

NAME
     std::pop_heap - std::pop_heap

Synopsis
	Defined in header <algorithm>
	template<  class RandomIt >				  (1) (constexpr
     since C++20)
	void pop_heap( RandomIt first, RandomIt last );
	template< class RandomIt, class Compare >
	void pop_heap( RandomIt first, RandomIt last, Compare	 (2)  (constexpr
     since C++20)
	comp );

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

	1) [first, last) is a heap with respect to
	operator<
	(until C++20)
	std::less{}
	(since C++20).
	2) [first, last) is a heap with respect to comp.

	If [first, last) not a non-empty heap, the behavior is undefined.

	If  any  of the following conditions is satisfied, the behavior is unde-
     fined:

	  * [first, last) is empty.
	  * [first, last) is not a heap.

	  * The type of *first is not Swappable.	   (until C++11)
	  * RandomIt is not ValueSwappable.
	  * The type of *first is not MoveConstructible.   (since C++11)
	  * The type of *first is not MoveAssignable.

Parameters
	first, last -  the non-empty heap to modify
		       comparison function object (i.e. an object that satisfies
     the
		       requirements of Compare) which returns true if the  first
     argument is
		       less than the second.

		       The signature of the comparison function should be equiv-
     alent to the
		       following:

		       bool cmp(const Type1& a, const Type2& b);
	comp	    -
		       While  the  signature  does  not need to have const&, the
     function must
		       not modify the objects passed to it and must be	able  to
     accept all
		       values  of  type (possibly const) Type1 and Type2 regard-
     less of value
		       category (thus, Type1& is not allowed
		       , nor is Type1 unless for Type1 a move is equivalent to a
     copy
		       (since C++11)).
		       The types Type1 and Type2 must be such that an object  of
     type
		       RandomIt  can  be  dereferenced	and then implicitly con-
     verted to both of
		       them.

Type requirements
	-
	RandomIt must meet the requirements of LegacyRandomAccessIterator.
	-
	Compare must meet the requirements of Compare.

Complexity
	Given \(\scriptsize N\)N as std::distance(first, last):

	1) At most \(\scriptsize 2\log(N)\)2log(N) comparisons using
	operator<
	(until C++20)
	std::less{}
	(since C++20).
	2) At most \(\scriptsize 2\log(N)\)2log(N) applications of the	compari-
     son function
	comp.

Example
     // Run this code

      #include <algorithm>
      #include <iostream>
      #include <string_view>
      #include <type_traits>
      #include <vector>

      void println(std::string_view rem, const auto& v)
      {
	  std::cout << rem;
	  if constexpr (std::is_scalar_v<std::decay_t<decltype(v)>>)
	      std::cout << v;
	  else
	      for (int e : v)
		  std::cout << e << ' ';
	  std::cout << '\n';
      }

      int main()
      {
	  std::vector<int> v{3, 1, 4, 1, 5, 9};

	  std::make_heap(v.begin(), v.end());
	  println("after make_heap: ", v);

	  std::pop_heap(v.begin(), v.end()); // moves the largest to the end
	  println("after pop_heap:  ", v);

	  int largest = v.back();
	  println("largest element: ", largest);

	  v.pop_back(); // actually removes the largest element
	  println("after pop_back:  ", v);
      }

Output:
      after make_heap: 9 5 4 1 1 3
      after pop_heap:  5 3 4 1 1 9
      largest element: 9
      after pop_back:  5 3 4 1 1

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	    Behavior as  published		 Correct
     behavior
	LWG  1205 C++98      the behavior was unclear if	    the behavior
     is undefined
			    [first, last) is empty		   in this case

See also
	push_heap	 adds an element to a max heap
			 (function template)
	is_heap 	 checks if the given range is a max heap
	(C++11) 	 (function template)
	is_heap_until	 finds the largest subrange that is a max heap
	(C++11) 	 (function template)
	make_heap	 creates a max heap out of a range of elements
			 (function template)
	sort_heap	 turns a max heap into a range of elements sorted in as-
     cending order
			 (function template)
	ranges::pop_heap removes the largest element from a max heap
	(C++20) 	 (niebloid)

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