std::ranges::minmax_element, std::ranges::minmax_element_result

Defined in header `<algorithm>`
Call signature
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less > constexpr minmax_element_result<I> minmax_element( I first, S last, Comp comp = {}, Proj proj = {} );	(1)	(since C++20)
template< ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less > constexpr minmax_element_result<ranges::borrowed_iterator_t<R>> minmax_element( R&& r, Comp comp = {}, Proj proj = {} );	(2)	(since C++20)
Helper types
template< class I > using minmax_element_result = ranges::min_max_result<I>;	(3)	(since C++20)

1) Finds the smallest and largest elements in the range [first, last).

2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

Explicit template argument lists may not be specified when calling any of them.
None of them is visible to argument-dependent lookup.
When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

first, last	-	iterator-sentinel pair denoting the range to examine
r	-	the range to examine
comp	-	comparison to apply to the projected elements
proj	-	projection to apply to the elements.

Return value

An object consisting of an iterator to the smallest element as the first element and an iterator to the greatest element as the second. Returns {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 comparison and twice as many applications of the projection, where N = ranges::distance(first, last).

Possible implementation

struct minmax_element_fn {
  template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
           std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
  constexpr ranges::minmax_element_result<I>
  operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
  {
    auto min = first, max = first;
 
    if (first == last || ++first == last) {
      return {min, max};
    }
 
    if (std::invoke(comp, std::invoke(proj, *first), std::invoke(proj, *min))) {
      min = first;
    } else {
      max = first;
    }
 
    while (++first != last) {
      auto i = first;
      if (++first == last) {
        if (std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, *min))) {
            min = i;
        }
        else if (!(std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, *max)))) {
            max = i;
        }
        break;
      } else {
        if (std::invoke(comp, std::invoke(proj, *first), std::invoke(proj, *i))) {
          if (std::invoke(comp, std::invoke(proj, *first), std::invoke(proj, *min))) {
            min = first;
          }
          if (!(std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, *max)))) {
            max = i;
          }
        } else {
          if (std::invoke(comp, std::invoke(proj, *i), std::invoke(proj, *min))) {
            min = i;
          }
          if (!(std::invoke(comp, std::invoke(proj, *first), std::invoke(proj, *max)))) {
            max = first;
          }
        }
      }
    }
    return {min, max};
  }
 
  template<ranges::forward_range R, class Proj = std::identity,
           std::indirect_strict_weak_order<
               std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
  constexpr ranges::minmax_element_result<ranges::borrowed_iterator_t<R>>
  operator()(R&& r, Comp comp = {}, Proj proj = {}) const
  {
    return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
  }
};
 
inline constexpr minmax_element_fn minmax_element;

Example

Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
namespace rng = std::ranges;
 
int main() {
    const auto v = { 3, 9, 1, 4, 1, 2, 5, 9 };
    const auto [min, max] = rng::minmax_element(v);
    std::cout
        << "min = " << *min << ", at [" << rng::distance(v.begin(), min) << "]\n"
        << "max = " << *max << ", at [" << rng::distance(v.begin(), max) << "]\n";
}

Output:

min = 1, at [2]
max = 9, at [7]

Compiler support
Freestanding and hosted
Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Technical specifications
Symbols index
External libraries

ranges::min_element (C++20)	returns the smallest element in a range (niebloid)
ranges::max_element (C++20)	returns the largest element in a range (niebloid)
ranges::minmax (C++20)	returns the smaller and larger of two elements (niebloid)
minmax_element (C++11)	returns the smallest and the largest elements in a range (function template)