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 details.
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 equivalent 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 converted 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 smallest 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(⌊

3
2

(N-1)⌋,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(⌊

3
2

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

Exceptions¶

The overloads with a template parameter named ExecutionPolicy report errors 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-defined.
* 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<ForwardIt>::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 algorithm 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)