Namespaces
Variants
Views
Actions

std::minmax_element

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
minmax_element
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
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)
template< class ExecutionPolicy, class ForwardIt >

constexpr std::pair<ForwardIt,ForwardIt>

    minmax_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );
(2) (since C++17)
(3)
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)
template< class ExecutionPolicy, class ForwardIt, class Compare >

constexpr 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<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Contents

[edit] Parameters

first, last - forward iterators defining the range to examine
policy - the execution policy to use. See execution policy for details.
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.

[edit] 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.

[edit] Complexity

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

[edit] 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,
  • if policy is std::parallel_vector_execution_policy, std::terminate is called
  • if policy is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.
  • if policy is some other type, the behavior is implementation-defined
  • If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.

[edit] 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.

[edit] 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;
}

[edit] 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

[edit] See also

returns the smallest element in a range
(function template) [edit]
returns the largest element in a range
(function template) [edit]
parallelized version of std::minmax_element
(function template) [edit]