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

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< cpp‎ | algorithm
(Uses {{mark constexpr since c++17}}.)
 
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{{cpp/algorithm/navbar}}
 
{{cpp/algorithm/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl header | algorithm}}
+
{{dcl header|algorithm}}
−
{{dcl | num=1 | since=c++11 |
+
{{dcla|num=1|since=c++11|notes={{mark constexpr since c++17}}|
−
template< class ForwardIt >  
+
template< class ForwardIt >
−
std::pair<ForwardIt,ForwardIt>  
+
std::pair<ForwardIt, ForwardIt>
 
     minmax_element( ForwardIt first, ForwardIt last );
 
     minmax_element( ForwardIt first, ForwardIt last );
 
}}
 
}}
−
{{dcl | num=2 | since=c++11 |
+
{{dcl|num=2|since=c++17|
 +
template< class ExecutionPolicy, class ForwardIt >
 +
std::pair<ForwardIt, ForwardIt>
 +
    minmax_element( ExecutionPolicy&& policy,
 +
                    ForwardIt first, ForwardIt last );
 +
}}
 +
{{dcla|num=3|since=c++11|notes={{mark constexpr since c++17}}|
 
template< class ForwardIt, class Compare >
 
template< class ForwardIt, class Compare >
−
std::pair<ForwardIt,ForwardIt>  
+
std::pair<ForwardIt, ForwardIt>
 
     minmax_element( ForwardIt first, ForwardIt last, Compare comp );
 
     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}}
 
{{dcl end}}
  
−
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}}.
+
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}}.
 +
 
 +
@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}.
 +
@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | first, last | forward iterators defining the range to examine}}
+
{{par|first, last|forward iterators defining the range to examine}}
−
{{par cmp | cmp | p1=ForwardIt | if {{tt|*a}} is ''less'' than {{tt|*b}}}}
+
{{par exec pol}}
 +
{{par cmp|cmp|p1=ForwardIt}}
 
{{par hreq}}
 
{{par hreq}}
−
{{par req concept | ForwardIt | ForwardIterator}}  
+
{{par req named|ForwardIt|ForwardIterator}}
 
{{par end}}
 
{{par end}}
  
Line 29: Line 49:
  
 
===Complexity===
 
===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)}}:
  
−
===Notes===
+
@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{}<!---->}}}}.
−
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.
+
 
 +
@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===
 
===Possible implementation===
−
{{eq fun
+
{{eq impl
−
| 1=
+
|title1=minmax_element|ver1=1|1=
 
template<class ForwardIt>
 
template<class ForwardIt>
−
std::pair<ForwardIt, ForwardIt>  
+
std::pair<ForwardIt, ForwardIt>
 
     minmax_element(ForwardIt first, ForwardIt last)
 
     minmax_element(ForwardIt first, ForwardIt last)
 
{
 
{
−
     return std::minmax_element(first, last, std::less<>());
+
    using value_type = typename std::iterator_traits<ForwardIt>::value_type;
 +
     return std::minmax_element(first, last, std::less<value_type>());
 
}
 
}
−
| 2=
+
|title2=minmax_element|ver2=3|2=
 
template<class ForwardIt, class Compare>
 
template<class ForwardIt, class Compare>
−
std::pair<ForwardIt, ForwardIt>  
+
std::pair<ForwardIt, ForwardIt>
 
     minmax_element(ForwardIt first, ForwardIt last, Compare comp)
 
     minmax_element(ForwardIt first, ForwardIt last, Compare comp)
 
{
 
{
−
     std::pair<ForwardIt, ForwardIt> 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.first = first;
+
         min = first;
−
     } else {
+
     else
−
         result.second = first;
+
         max = first;
−
     }
+
      
−
     while (++first != last) {
+
     while (++first != last)
−
         ForwardIt i = first;
+
    {
−
         if (++first == last) {
+
         auto i = first;
−
             if (comp(*i, *result.first)) result.first = i;
+
         if (++first == last)
−
             else if (!(comp(*i, *result.second))) result.second = i;
+
        {
 +
             if (comp(*i, *min))
 +
                min = i;
 +
             else if (!(comp(*i, *max)))
 +
                max = i;
 
             break;
 
             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===
 
{{example
 
{{example
−
|
+
|
−
| code=
+
|code=
 
#include <algorithm>
 
#include <algorithm>
 
#include <iostream>
 
#include <iostream>
−
#include <vector>
 
 
   
 
   
 
int main()
 
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===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/algorithm/dsc min_element}}
+
{{dsc inc|cpp/algorithm/dsc min_element}}
−
{{dsc inc | cpp/algorithm/dsc max_element}}
+
{{dsc inc|cpp/algorithm/dsc max_element}}
 +
{{dsc inc|cpp/algorithm/ranges/dsc minmax_element}}
 
{{dsc end}}
 
{{dsc end}}
  
−
[[de:cpp/algorithm/minmax element]]
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
[[es:cpp/algorithm/minmax element]]
+
−
[[fr:cpp/algorithm/minmax element]]
+
−
[[it:cpp/algorithm/minmax element]]
+
−
[[ja:cpp/algorithm/minmax element]]
+
−
[[pt:cpp/algorithm/minmax element]]
+
−
[[ru:cpp/algorithm/minmax element]]
+
−
[[zh:cpp/algorithm/minmax element]]
+

Latest revision as of 18:20, 9 April 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
minmax_element
(C++11)

Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
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)

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

1,2) At most max(⌊
3
2
(N-1)⌋,0) comparisons using operator<(until C++20)std::less{}(since C++20).
3,4) At most max(⌊
3
2
(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

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