Difference between revisions of "cpp/algorithm/minmax element"

Latest revision as of 18:20, 9 April 2024

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

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)

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 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.

[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

Given $\scriptsize N$ $N$ as std::distance(first, last):

1,2) At most

max(⌊ 32 (N-1)⌋,0)

comparisons using operator<(until C++20)std::less{}(since C++20).

3,4) At most

max(⌊ 32 (N-1)⌋,0)

applications of the comparison function comp.

[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 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.

[edit] 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};
}

[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] 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

[edit] See also

min_element	returns the smallest element in a range (function template) [edit]
max_element	returns the largest element in a range (function template) [edit]
ranges::minmax_element (C++20)	returns the smallest and the largest elements in a range (niebloid)[edit]

@@ Line 3: / Line 3: @@
 {{dcl begin}}
 {{dcl header|algorithm}}
-{{dcl rev begin|num=1}}
+{{dcla|num=1|since=c++11|notes={{mark constexpr since c++17}}|
-{{dcla|since=c++11|until=c++17|anchor=1|
 template< class ForwardIt >
 std::pair<ForwardIt, ForwardIt>
      minmax_element( ForwardIt first, ForwardIt last );
 }}
-{{dcl|since=c++17|1=
+{{dcl|num=2|since=c++17|
-template< class ForwardIt >
-constexpr std::pair<ForwardIt, ForwardIt>
-    minmax_element( ForwardIt first, ForwardIt last );
-}}
-{{dcl rev end}}
-{{dcl|since=c++17|num=2|1=
 template< class ExecutionPolicy, class ForwardIt >
 std::pair<ForwardIt, ForwardIt>
-     minmax_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );}}
+     minmax_element( ExecutionPolicy&& policy,
-{{dcl rev begin|num=3}}
+                    ForwardIt first, ForwardIt last );
-{{dcla|since=c++11|until=c++17|anchor=3|
+}}
+{{dcla|num=3|since=c++11|notes={{mark constexpr since c++17}}|
 template< class ForwardIt, class Compare >
 std::pair<ForwardIt, ForwardIt>
      minmax_element( ForwardIt first, ForwardIt last, Compare comp );
 }}
-{{dcl|since=c++17|1=
+{{dcl|num=4|since=c++17|
-template< class ForwardIt, class Compare >
-constexpr std::pair<ForwardIt, ForwardIt>
-    minmax_element( ForwardIt first, ForwardIt last, Compare comp );
-}}
-{{dcl rev end}}
-{{dcl|since=c++17|num= 4|1=
 template< class ExecutionPolicy, class ForwardIt, class Compare >
 std::pair<ForwardIt, ForwardIt>
      minmax_element( ExecutionPolicy&& policy,
-                     ForwardIt first, ForwardIt last, Compare comp );}}
+                     ForwardIt first, ForwardIt last, Compare comp );
+}}
 {{dcl end}}
 Finds the smallest and greatest element in the range {{range|first|last}}.
-@1@ Elements are compared using {{tt|operator<}}.
+@1@ Elements are compared using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
-@3@ Elements are compared using the given binary comparison function {{c|comp}}.
-@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
+@3@ Elements are compared using the comparison function {{c|comp}}.
+@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
+@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
 ===Parameters===
@@ Line 48: / Line 40: @@
 {{par|first, last|forward iterators defining the range to examine}}
 {{par exec pol}}
-{{par cmp|cmp|p1=ForwardIt|{{c|*a}} is ''less'' than {{c|*b}}}}
+{{par cmp|cmp|p1=ForwardIt}}
 {{par hreq}}
 {{par req named|ForwardIt|ForwardIterator}}
@@ Line 57: / Line 49: @@
 ===Complexity===
-At most {{math|max(floor((3/2)*(N−1)), 0)}} applications of the predicate, where {{c|N {{=}} std::distance(first, last)}}.
+Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
+@1,2@ At most {{mathjax-or|\(\scriptsize \max(\left\lfloor \frac{3}{2}(N-1) \right\rfloor, 0)\)|max(⌊{{mfrac|3|2}}(N-1)⌋,0)}} comparisons using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
+@3,4@ At most {{mathjax-or|\(\scriptsize \max(\left\lfloor \frac{3}{2}(N-1) \right\rfloor, 0)\)|max(⌊{{mfrac|3|2}}(N-1)⌋,0)}} applications of the comparison function {{c|comp}}.
 ===Exceptions===
-{{cpp/algorithm/parallel_exceptions_reporting_behavior|singular=no}}
+{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
-===Notes===
-This algorithm is different from {{c|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 {{lc|std::max_element}} finds the ''first'' biggest element.
 ===Possible implementation===
@@ Line 81: / Line 74: @@
 {
      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)
      {
@@ Line 122: / Line 115: @@
 }
 }}
+===Notes===
+This algorithm is different from {{c|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 {{lc|std::max_element}} finds the ''first'' biggest element.
 ===Example===

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Difference between revisions of "cpp/algorithm/minmax element"

Latest revision as of 18:20, 9 April 2024

Contents

[edit] Parameters