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std::ranges::max_element() algorithm

// (1)
constexpr I max_element( I first, S last, Comp comp = {}, Proj proj = {} );

// (2)
constexpr ranges::borrowed_iterator_t<R>
max_element( R&& r, Comp comp = {}, Proj proj = {} );

The type of arguments are generic and have the following constraints:

  • I - std::forward_iterator
  • S - std::sentinel_for<I>
  • R - std::ranges::forward_range
  • Comp:
    • (1) - std::indirect_strict_weak_order<std::projected<I, Proj>>
    • (2) - std::indirect_strict_weak_order<std::projected<ranges::iterator_t<R>, Proj>>
  • Proj - (none)

The Proj and Comp template arguments have the following default types: std::identity, ranges::less for all overloads.

Additionally, each overload has the following constraints:

  • (1) - std::sortable<I, Comp, Proj>
  • (2) - std::sortable<ranges::iterator_t<R>, Comp, Proj>
  • (1) Finds the greatest element 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.

Parameters

first
last

The range to find the largest value in.

r

The range to find the largest value in.

comp

Comparison to apply to the projected elements.

proj

Projection to apply to the elements.

Return value

Iterator to the greatest element in the range [first; last).

If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element.

Returns first if the range is empty.

Complexity

Given N as std::distance(first, last):

Exactly max(N - 1, 0) comparisons.

Exceptions

(none)

Possible implementation

max_element(1) and max_element(2)

struct max_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 I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
{
if (first == last)
return last;

auto largest = first;
++first;
for (; first != last; ++first)
if (std::invoke(comp, std::invoke(proj, *largest), std::invoke(proj, *first)))
largest = first;
return largest;
}

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::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 max_element_fn max_element;

Examples

Main.cpp
#include <algorithm>
#include <cmath>
#include <iostream>
#include <vector>

int main()
{
std::vector<int> v {3, 1, -14, 1, 5, 9};

namespace ranges = std::ranges;
auto result = ranges::max_element(v.begin(), v.end());
std::cout << "max element at: " << ranges::distance(v.begin(), result) << '\n';

auto abs_compare = [](int a, int b) { return (std::abs(a) < std::abs(b)); };
result = ranges::max_element(v, abs_compare);
std::cout << "max element (absolute) at: " << ranges::distance(v.begin(), result) << '\n';
}
Output
max element at: 5
max element (absolute) at: 2
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::ranges::max_element() algorithm

// (1)
constexpr I max_element( I first, S last, Comp comp = {}, Proj proj = {} );

// (2)
constexpr ranges::borrowed_iterator_t<R>
max_element( R&& r, Comp comp = {}, Proj proj = {} );

The type of arguments are generic and have the following constraints:

  • I - std::forward_iterator
  • S - std::sentinel_for<I>
  • R - std::ranges::forward_range
  • Comp:
    • (1) - std::indirect_strict_weak_order<std::projected<I, Proj>>
    • (2) - std::indirect_strict_weak_order<std::projected<ranges::iterator_t<R>, Proj>>
  • Proj - (none)

The Proj and Comp template arguments have the following default types: std::identity, ranges::less for all overloads.

Additionally, each overload has the following constraints:

  • (1) - std::sortable<I, Comp, Proj>
  • (2) - std::sortable<ranges::iterator_t<R>, Comp, Proj>
  • (1) Finds the greatest element 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.

Parameters

first
last

The range to find the largest value in.

r

The range to find the largest value in.

comp

Comparison to apply to the projected elements.

proj

Projection to apply to the elements.

Return value

Iterator to the greatest element in the range [first; last).

If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element.

Returns first if the range is empty.

Complexity

Given N as std::distance(first, last):

Exactly max(N - 1, 0) comparisons.

Exceptions

(none)

Possible implementation

max_element(1) and max_element(2)

struct max_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 I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
{
if (first == last)
return last;

auto largest = first;
++first;
for (; first != last; ++first)
if (std::invoke(comp, std::invoke(proj, *largest), std::invoke(proj, *first)))
largest = first;
return largest;
}

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::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 max_element_fn max_element;

Examples

Main.cpp
#include <algorithm>
#include <cmath>
#include <iostream>
#include <vector>

int main()
{
std::vector<int> v {3, 1, -14, 1, 5, 9};

namespace ranges = std::ranges;
auto result = ranges::max_element(v.begin(), v.end());
std::cout << "max element at: " << ranges::distance(v.begin(), result) << '\n';

auto abs_compare = [](int a, int b) { return (std::abs(a) < std::abs(b)); };
result = ranges::max_element(v, abs_compare);
std::cout << "max element (absolute) at: " << ranges::distance(v.begin(), result) << '\n';
}
Output
max element at: 5
max element (absolute) at: 2
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.