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 1: / Line 1: @@
 {{cpp/title|minmax_element}}
 {{cpp/algorithm/navbar}}
-{{ddcl list begin}}
+{{dcl begin}}
-{{ddcl list header | algorithm}}
+{{dcl header|algorithm}}
-{{ddcl list item | num=1 |
+{{dcla|num=1|since=c++11|notes={{mark constexpr since c++17}}|
-template< class ForwardIterator >
+template< class ForwardIt >
-std::pair<ForwardIterator,ForwardIterator>
+std::pair<ForwardIt, ForwardIt>
-     minmax_element( ForwardIterator first, ForwardIterator last );
+     minmax_element( ForwardIt first, ForwardIt last );
 }}
-{{ddcl list item | num=2 |
+{{dcl|num=2|since=c++17|
-template< class ForwardIterator, class Compare >
+template< class ExecutionPolicy, class ForwardIt >
-std::pair<ForwardIterator,ForwardIterator>
+std::pair<ForwardIt, ForwardIt>
-     minmax_element( ForwardIterator first, ForwardIterator last,
+     minmax_element( ExecutionPolicy&& policy,
-                     Compare comp );
+                     ForwardIt first, ForwardIt last );
 }}
-{{ddcl list end}}
+{{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|num=4|since=c++17|
+template< class ExecutionPolicy, class ForwardIt, class Compare >
+std::pair<ForwardIt, ForwardIt>
+    minmax_element( ExecutionPolicy&& policy,
+                    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 {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
+@3@ Elements are compared using the comparison function {{c|comp}}.
-Finds the greatest and the smallest element in the range {{tt|[first, last)}}. The first version uses {{c|operator<}} to compare the values, the second version uses the given comparison function {{tt|comp}}.
+@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
+@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
 ===Parameters===
-{{param list begin}}
+{{par begin}}
-{{param list item | first, last | forward iterators defining the range to examine}}
+{{par|first, last|forward iterators defining the range to examine}}
-{{param list cmp | cmp | p1=ForwardIterator | if {{tt|*a}} is ''less'' than {{tt|*b}}}}
+{{par exec pol}}
-{{param list end}}
+{{par cmp|cmp|p1=ForwardIt}}
+{{par hreq}}
+{{par req named|ForwardIt|ForwardIterator}}
+{{par end}}
 ===Return value===
@@ Line 28: / 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}}
 ===Possible implementation===
-{{eq fun
+{{eq impl
- | 1=
+|title1=minmax_element|ver1=1|1=
-template<class ForwardIterator>
+template<class ForwardIt>
-std::pair<ForwardIterator, ForwardIterator>
+std::pair<ForwardIt, ForwardIt>
-     minmax_element(ForwardIterator first, ForwardIterator last)
+     minmax_element(ForwardIt first, ForwardIt last)
 {
-     typedef typename std::iterator_traits<ForwardIterator>::value_type value_t;
+     using value_type = typename std::iterator_traits<ForwardIt>::value_type;
-     return std::minmax_element(first, last, std::less<value_t>());
+     return std::minmax_element(first, last, std::less<value_type>());
 }
- | 2=
+|title2=minmax_element|ver2=3|2=
-template<class ForwardIterator, class Compare>
+template<class ForwardIt, class Compare>
-std::pair<ForwardIterator, ForwardIterator>
+std::pair<ForwardIt, ForwardIt>
-     minmax_element(ForwardIterator first, ForwardIterator last, Compare comp)
+     minmax_element(ForwardIt first, ForwardIt last, Compare comp)
 {
-     std::pair<ForwardIterator, ForwardIterator> result(first, first);
+     auto min = first, max = first;
-     if (first == last) return result;
+     if (first == last {{!!}} ++first == last)
-    if (++first == last) return result;
+        return {min, max};
-     if (comp(*first, *result.first)) {
+     if (comp(*first, *min))
-         result.second = result.first;
+         min = first;
-        result.first = first;
+     else
-     } else {
+         max = first;
-         result.second = first;
-     }
+     while (++first != last)
-     while (++first != last) {
+    {
-         ForwardIterator i = first;
+         auto i = first;
-         if (++first == last) {
+         if (++first == last)
-             if (comp(*i, *result.first)) result.first = i;
+        {
-             else if (!(comp(*i, *result.second))) result.second = i;
+             if (comp(*i, *min))
+                min = i;
+             else if (!(comp(*i, *max)))
+                max = i;
              break;
-         } else {
+         }
-             if (comp(*first, *i)) {
+        else
-                 if (comp(*first, *result.first)) result.first = first;
+        {
-                 if (!(comp(*i, *result.second))) result.second = i;
+             if (comp(*first, *i))
-             } else {
+            {
-                 if (comp(*i, *result.first)) result.first = i;
+                 if (comp(*first, *min))
-                 if (!(comp(*first, *result.second))) result.second = first;
+                    min = first;
+                 if (!(comp(*i, *max)))
+                    max = i;
+             }
+            else
+            {
+                 if (comp(*i, *min))
+                    min = i;
+                 if (!(comp(*first, *max)))
+                    max = first;
              }
          }
      }
-     return result;
+     return {min, max};
 }
 }}
+===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===
 {{example
- |
+|
- | code=
+|code=
 #include <algorithm>
 #include <iostream>
-#include <vector>
 int main()
 {
-     std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 };
+     const auto v = {3, 9, 1, 4, 2, 5, 9};
+     const auto [min, max] = std::minmax_element(begin(v), end(v));
-     auto result = std::minmax_element(v.begin(), v.end());
-     std::cout << "min element at: " << (result.first - v.begin()) << '\n';
+     std::cout << "min = " << *min << ", max = " << *max << '\n';
-    std::cout << "max element at: " << (result.second - v.begin()) << '\n';
 }
- | output=
+|output=
-min element at: 2
+min = 1, max = 9
-max element at: 6
 }}
 ===See also===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/algorithm/dcl list min_element}}
+{{dsc inc|cpp/algorithm/dsc min_element}}
-{{dcl list template | cpp/algorithm/dcl list max_element}}
+{{dsc inc|cpp/algorithm/dsc max_element}}
-{{dcl list end}}
+{{dsc inc|cpp/algorithm/ranges/dsc minmax_element}}
+{{dsc end}}
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

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

Latest revision as of 18:20, 9 April 2024

Contents

[edit] Parameters