std::minmax_element

Defined in header `<algorithm>`
	(1)
template< class ForwardIt > std::pair<ForwardIt,ForwardIt> minmax_element( ForwardIt first, ForwardIt last );		(since C++11) (until C++17)
template< class ForwardIt > constexpr std::pair<ForwardIt,ForwardIt> minmax_element( ForwardIt first, ForwardIt last );		(since C++17)
		(2)
template< class ForwardIt, class Compare > std::pair<ForwardIt,ForwardIt> minmax_element( ForwardIt first, ForwardIt last, Compare comp );			(since C++11) (until C++17)
template< class ForwardIt, class Compare > constexpr std::pair<ForwardIt,ForwardIt> minmax_element( ForwardIt first, ForwardIt last, Compare comp );			(since C++17)

Finds the greatest and the smallest element in the range [first, last). The first version uses operator< to compare the values, the second version uses the given comparison function comp.

Parameters

first, last	-	forward iterators defining the range to examine
cmp	-	comparison function object (i.e. an object that satisfies the requirements of `Compare`) which returns `true` if if `a` is less* than `*b`. The signature of the comparison function should be equivalent to the following: `bool cmp(const Type1 &a, const Type2 &b);` The signature does not need to have `const &`, but the function object must not modify the objects passed to it. 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 `ForwardIterator`.

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

At most max(floor(3/2(N−1)), 0) applications of the predicate, where N = std::distance(first, last).

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.

Possible implementation

First version
template<class ForwardIt> std::pair<ForwardIt, ForwardIt> minmax_element(ForwardIt first, ForwardIt last) { return std::minmax_element(first, last, std::less<>()); }
Second version
template<class ForwardIt, class Compare> std::pair<ForwardIt, ForwardIt> minmax_element(ForwardIt first, ForwardIt last, Compare comp) { std::pair<ForwardIt, ForwardIt> result(first, first); if (first == last) return result; if (++first == last) return result; if (comp(first, result.first)) { result.first = first; } else { result.second = first; } while (++first != last) { ForwardIt i = first; if (++first == last) { if (comp(i, result.first)) result.first = i; else if (!(comp(i, result.second))) result.second = i; break; } else { if (comp(first, i)) { if (comp(first, result.first)) result.first = first; if (!(comp(i, result.second))) result.second = i; } else { if (comp(i, result.first)) result.first = i; if (!(comp(first, result.second))) result.second = first; } } } return result; }

First version

template<class ForwardIt>
std::pair<ForwardIt, ForwardIt> 
    minmax_element(ForwardIt first, ForwardIt last)
{
    return std::minmax_element(first, last, std::less<>());
}

Second version

template<class ForwardIt, class Compare>
std::pair<ForwardIt, ForwardIt> 
    minmax_element(ForwardIt first, ForwardIt last, Compare comp)
{
    std::pair<ForwardIt, ForwardIt> result(first, first);
 
    if (first == last) return result;
    if (++first == last) return result;
 
    if (comp(*first, *result.first)) {
        result.first = first;
    } else {
        result.second = first;
    }
    while (++first != last) {
        ForwardIt i = first;
        if (++first == last) {
            if (comp(*i, *result.first)) result.first = i;
            else if (!(comp(*i, *result.second))) result.second = i;
            break;
        } else {
            if (comp(*first, *i)) {
                if (comp(*first, *result.first)) result.first = first;
                if (!(comp(*i, *result.second))) result.second = i;
            } else {
                if (comp(*i, *result.first)) result.first = i;
                if (!(comp(*first, *result.second))) result.second = first;
            }
        }
    }
    return result;
}

Example

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 };
 
    auto result = std::minmax_element(v.begin(), v.end());
    std::cout << "min element at: " << (result.first - v.begin()) << '\n';
    std::cout << "max element at: " << (result.second - v.begin()) << '\n';
}

Output:

min element at: 2
max element at: 6

min_element	returns the smallest element in a range (function template)
max_element	returns the largest element in a range (function template)
std::experimental::parallel::minmax_element (parallelism TS)	parallelized version of `std::minmax_element` (function template)