# std::minmax_element

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class ForwardIt > std::pair <ForwardIt, ForwardIt> minmax_element( ForwardIt first, ForwardIt last ); | (1) | (since C++11) (constexpr since C++17)
template< class ExecutionPolicy, class ForwardIt > std::pair <ForwardIt, ForwardIt> minmax_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last ); | (2) | (since C++17)
template< class ForwardIt, class Compare > std::pair <ForwardIt, ForwardIt> minmax_element( ForwardIt first, ForwardIt last, Compare comp ); | (3) | (since C++11) (constexpr since C++17)
template< class ExecutionPolicy, class ForwardIt, class Compare > std::pair <ForwardIt, ForwardIt> minmax_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Compare comp ); | (4) | (since C++17)

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 all following conditions are satisfied:

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

cmp

-

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);

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 (C++20) | returns the smallest and the largest elements in a range (algorithm function object)

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