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

Latest revision as of 18:09, 9 April 2024

Defined in header `<algorithm>`
template< class ForwardIt > ForwardIt min_element( ForwardIt first, ForwardIt last );	(1)	(constexpr since C++17)
template< class ExecutionPolicy, class ForwardIt > ForwardIt min_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );	(2)	(since C++17)
template< class ForwardIt, class Compare > ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );	(3)	(constexpr since C++17)
template< class ExecutionPolicy, class ForwardIt, class Compare > ForwardIt min_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Compare comp );	(4)	(since C++17)

Finds the smallest 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.
comp	-	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

Iterator to the smallest element in the range [first, last). If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns last if the range is empty.

[edit] Complexity

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

1,2) Exactly

max(N-1,0)

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

3,4) Exactly

max(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

min_element (1)

template<class ForwardIt>
ForwardIt min_element(ForwardIt first, ForwardIt last)
{
    if (first == last)
        return last;
 
    ForwardIt smallest = first;
 
    while (++first != last)
        if (*first < *smallest)
            smallest = first;
 
    return smallest;
}

min_element (3)

template<class ForwardIt, class Compare>
ForwardIt min_element(ForwardIt first, ForwardIt last, Compare comp)
{
    if (first == last)
        return last;
 
    ForwardIt smallest = first;
 
    while (++first != last)
        if (comp(*first, *smallest))
            smallest = first;
 
    return smallest;
}

[edit] Example

Run this code

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, 1, -4, 1, 5, 9};
 
    std::vector<int>::iterator result = std::min_element(v.begin(), v.end());
    std::cout << "min element has value " << *result << " and index ["
              << std::distance(v.begin(), result) << "]\n";
}

Output:

min element has value -4 and index [2]

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 212	C++98	the return value was not specified if `[`first`,` last`)` is empty	returns last in this case
LWG 2150	C++98	the iterator to the first non-greatest element was returned	corrected the return value

[edit] See also

max_element	returns the largest element in a range (function template) [edit]
minmax_element (C++11)	returns the smallest and the largest elements in a range (function template) [edit]
min	returns the smaller of the given values (function template) [edit]
ranges::min_element (C++20)	returns the smallest element in a range (niebloid)[edit]

@@ Line 1: / Line 1: @@
 {{cpp/title|min_element}}
 {{cpp/algorithm/navbar}}
-{{ddcl list begin}}
+{{dcl begin}}
-{{ddcl list header | algorithm}}
+{{dcl header|algorithm}}
-{{ddcl list item | num=1 |
+{{dcla|num=1|notes={{mark constexpr since c++17}}|
-template< class ForwardIterator >
+template< class ForwardIt >
-ForwardIterator min_element( ForwardIterator first, ForwardIterator last );
+ForwardIt min_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 >
-ForwardIterator min_element( ForwardIterator first, ForwardIterator last,
+ForwardIt min_element( ExecutionPolicy&& policy,
-                             Compare comp );
+                       ForwardIt first, ForwardIt last );
 }}
-{{ddcl list end}}
+{{dcla|num=3|notes={{mark constexpr since c++17}}|
+template< class ForwardIt, class Compare >
+ForwardIt min_element( ForwardIt first, ForwardIt last,
+                       Compare comp );
+}}
+{{dcl|num=4|since=c++17|
+template< class ExecutionPolicy, class ForwardIt, class Compare >
+ForwardIt min_element( ExecutionPolicy&& policy,
+                       ForwardIt first, ForwardIt last,
+                       Compare comp );
+}}
+{{dcl end}}
+Finds the smallest 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 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|comp|p1=ForwardIt}}
+{{par hreq}}
+{{par req named|ForwardIt|ForwardIterator}}
+{{par end}}
 ===Return value===
-Iterator to the smallest element in the range {{tt|[first, last)}}. If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns {{tt|last}} if the range is empty.
+Iterator to the smallest element in the range {{range|first|last}}. If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns {{c|last}} if the range is empty.
 ===Complexity===
-Exactly {{math|max(N-1,0)}} comparisons, where {{c|N {{=}} std::distance(first, last)}}.
+Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|std::distance(first, last)}}:
+@1,2@ Exactly {{mathjax-or|\(\scriptsize \max(N-1,0)\)|max(N-1,0)}} comparisons using {{rev inl|until=c++20|{{c/core|operator<}}}}{{rev inl|since=c++20|{{c|std::less{}<!---->}}}}.
+@3,4@ Exactly {{mathjax-or|\(\scriptsize \max(N-1,0)\)|max(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=min_element (1)|ver1=1|1=
-template<class ForwardIterator>
+template<class ForwardIt>
-ForwardIterator min_element(ForwardIterator first, ForwardIterator last)
+ForwardIt min_element(ForwardIt first, ForwardIt last)
 {
-     if (first == last) return last;
+     if (first == last)
+        return last;
-     ForwardIterator smallest = first;
-     ++first;
+     ForwardIt smallest = first;
-     for (; first != last; ++first) {
-         if (*first < *smallest) {
+     while (++first != last)
+         if (*first < *smallest)
              smallest = first;
-        }
-     }
      return smallest;
 }
- | 2=
+|title2=min_element (3)|ver2=3|2=
-template<class ForwardIterator, class Compare>
+template<class ForwardIt, class Compare>
-ForwardIterator min_element(ForwardIterator first, ForwardIterator last,
+ForwardIt min_element(ForwardIt first, ForwardIt last, Compare comp)
-                            Compare comp)
 {
-     if (first == last) return last;
+     if (first == last)
+        return last;
-     ForwardIterator smallest = first;
+     ForwardIt smallest = first;
-     ++first;
-     for (; first != last; ++first) {
+     while (++first != last)
-         if (comp(*first, *smallest)) {
+         if (comp(*first, *smallest))
              smallest = first;
-        }
-     }
+     return smallest;
-     return largest;
 }
 }}
@@ Line 65: / Line 92: @@
 ===Example===
 {{example
- |
+|
- | code=
+|code=
 #include <algorithm>
 #include <iostream>
@@ Line 73: / Line 100: @@
 int main()
 {
-     std::vector<int> v{3, 1, 4, 1, 5, 9};
+     std::vector<int> v{3, 1, -4, 1, 5, 9};
      std::vector<int>::iterator result = std::min_element(v.begin(), v.end());
-     std::cout << "min element at: " << std::distance(v.begin(), result);
+     std::cout << "min element has value " << *result << " and index ["
+              << std::distance(v.begin(), result) << "]\n";
 }
- | output=
+|output=
-min element at: 1
+min element has value -4 and index [2]
 }}
+===Defect reports===
+{{dr list begin}}
+{{dr list item|wg=lwg|dr=212|std=C++98|before=the return value was not specified if {{range|first|last}} is empty|after=returns {{c|last}} in this case}}
+{{dr list item|wg=lwg|dr=2150|std=C++98|before=the iterator to the first non-greatest element was returned|after=corrected the return value}}
+{{dr list end}}
 ===See also===
-{{dcl list begin}}
+{{dsc begin}}
-{{dcl list template | cpp/algorithm/dcl list max_element}}
+{{dsc inc|cpp/algorithm/dsc max_element}}
-{{dcl list template | cpp/algorithm/dcl list minmax_element}}
+{{dsc inc|cpp/algorithm/dsc minmax_element}}
-{{dcl list template | cpp/algorithm/dcl list min}}
+{{dsc inc|cpp/algorithm/dsc min}}
-{{dcl list end}}
+{{dsc inc|cpp/algorithm/ranges/dsc min_element}}
+{{dsc end}}
-[[es:cpp/algorithm/min element]]
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
-[[fr:cpp/algorithm/min element]]
-[[pt:cpp/algorithm/min element]]
-[[ru:cpp/algorithm/min element]]

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

Latest revision as of 18:09, 9 April 2024

Contents

[edit] Parameters