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

NAME
     std::minmax_element - std::minmax_element

Synopsis
	Defined in header <algorithm>
	template< class ForwardIt >
								     (since
     C++11)
	std::pair<ForwardIt,  ForwardIt>			  (1) (constexpr
     since C++17)

	    minmax_element( ForwardIt first, ForwardIt last );
	template< class ExecutionPolicy, class ForwardIt >

	std::pair<ForwardIt,  ForwardIt>			    (2)   (since
     C++17)
	    minmax_element( ExecutionPolicy&& policy,

			    ForwardIt first, ForwardIt last );
	template< class ForwardIt, class Compare >

	std::pair<ForwardIt,   ForwardIt>			     (3)  (since
     C++11)
								     (constexpr
     since C++17)
	    minmax_element( ForwardIt first, ForwardIt last,
	Compare comp );
	template< class ExecutionPolicy, class ForwardIt, class
	Compare >

	std::pair<ForwardIt,  ForwardIt>			    (4)   (since
     C++17)
	    minmax_element( ExecutionPolicy&& policy,

			    ForwardIt first, ForwardIt last,
	Compare comp );

	Finds the smallest and greatest element in the range [first, last).

	1) Elements are compared using
	operator<
	(until C++20)
	std::less{}
	(since C++20).
	3) Elements are compared using the comparison function comp.
	2,4) Same as (1,3), but executed according to policy.
	These overloads participate in overload resolution only if

	std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>    is    true.
     (until
										  C++20)
	std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>      is
     true. (since
										  C++20)

Parameters
	first, last - forward iterators defining the range to examine
	policy	     - the execution policy to use. See execution policy for de-
     tails.
		      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 equiva-
     lent to the
		      following:

		      bool cmp(const Type1& a, const Type2& b);
	cmp	    -
		      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 regardless
     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
		      ForwardIt can be dereferenced  and  then	implicitly  con-
     verted to both of
		      them.

Type requirements
	-
	ForwardIt must meet the requirements of LegacyForwardIterator.

Return value
	a  pair  consisting  of an iterator to the smallest element as the first
     element and an
	iterator   to	the   greatest	 element   as	the   second.	 Returns
     std::make_pair(first, first)
	if  the range is empty. If several elements are equivalent to the small-
     est element,
	the iterator to the first such element is returned. If several	elements
     are
	equivalent to the largest element, the iterator to the last such element
     is
	returned.

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

	1,2)	At   most   \(\scriptsize   \max(\left\lfloor	\frac{3}{2}(N-1)
     \right\rfloor,
	0)\)max(a

	3
	2

	(N-1)a,0) comparisons using
	operator<
	(until C++20)
	std::less{}
	(since C++20).
	3,4)   At   most   \(\scriptsize   \max(\left\lfloor	\frac{3}{2}(N-1)
     \right\rfloor,
	0)\)max(a

	3
	2

	(N-1)a,0) applications of the comparison function comp.

Exceptions
	The overloads with a template parameter named ExecutionPolicy report er-
     rors as
	follows:

	  *  If  execution of a function invoked as part of the algorithm throws
     an exception
	    and ExecutionPolicy is one of the standard policies,  std::terminate
     is called.
	    For  any  other  ExecutionPolicy, the behavior is implementation-de-
     fined.
	  * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation
				       minmax_element
	template<class ForwardIt>
	std::pair<ForwardIt, ForwardIt>
	    minmax_element(ForwardIt first, ForwardIt last)
	{
	    using    value_type     =	  typename     std::iterator_traits<For-
     wardIt>::value_type;
	    return std::minmax_element(first, last, std::less<value_type>());
	}
				       minmax_element
	template<class ForwardIt, class Compare>
	std::pair<ForwardIt, ForwardIt>
	    minmax_element(ForwardIt first, ForwardIt last, Compare comp)
	{
	    auto min = first, max = first;

	    if (first == last || ++first == last)
		return {min, max};

	    if (comp(*first, *min))
		min = first;
	    else
		max = first;

	    while (++first != last)
	    {
		auto i = first;
		if (++first == last)
		{
		    if (comp(*i, *min))
			min = i;
		    else if (!(comp(*i, *max)))
			max = i;
		    break;
		}
		else
		{
		    if (comp(*first, *i))
		    {
			if (comp(*first, *min))
			    min = first;
			if (!(comp(*i, *max)))
			    max = i;
		    }
		    else
		    {
			if (comp(*i, *min))
			    min = i;
			if (!(comp(*first, *max)))
			    max = first;
		    }
		}
	    }
	    return {min, max};
	}

Notes
	This algorithm is different from std::make_pair(std::min_element(),
	std::max_element()), not only in efficiency, but also in that this algo-
     rithm finds
	the  last biggest element while std::max_element finds the first biggest
     element.

Example
     // Run this code

      #include <algorithm>
      #include <iostream>

      int main()
      {
	  const auto v = {3, 9, 1, 4, 2, 5, 9};
	  const auto [min, max] = std::minmax_element(begin(v), end(v));

	  std::cout << "min = " << *min << ", max = " << *max << '\n';
      }

Output:
      min = 1, max = 9

See also
	min_element	       returns the smallest element in a range
			       (function template)
	max_element	       returns the largest element in a range
			       (function template)
	ranges::minmax_element returns the smallest and the largest elements  in
     a range
	(C++20) 	       (niebloid)

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