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std::minmax_element

Da cppreference.com.
< cpp‎ | algorithm

 
 
Algoritmo libreria
Funzioni
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Functions
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Non modifica le operazioni di sequenza
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Non-modifying sequence operations
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Modifica delle operazioni di sequenza
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Modifying sequence operations
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Partizionamento operazioni
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Partitioning operations
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Ordinamento delle operazioni (su intervalli ordinati)
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Sorting operations (on sorted ranges)
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Binarie (le operazioni di ricerca sui campi ordinati)
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Binary search operations (on sorted ranges)
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Impostare le operazioni (su intervalli ordinati)
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Set operations (on sorted ranges)
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Heap operazioni
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Heap operations
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Minimo / massimo le operazioni
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Minimum/maximum operations
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max
max_element
min
min_element
minmax(C++11)
minmax_element(C++11)
Operazioni numeriche
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Numeric operations
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Libreria C
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C library
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Defined in header <algorithm>
template< class ForwardIt >

std::pair<ForwardIt,ForwardIt>

    minmax_element( ForwardIt first, ForwardIt last );
(1)
template< class ForwardIt, class Compare >

std::pair<ForwardIt,ForwardIt>

    minmax_element( ForwardIt first, ForwardIt last, Compare comp );
(2)
Trova il più grande e il più piccolo elemento nel [first, last) gamma. La prima versione utilizza operator< per confrontare i valori, la seconda versione utilizza la funzione di confronto dato comp.
Original:
Finds the greatest and the smallest element in the range [first, last). The first version uses operator< to compare the values, the second version uses the given comparison function comp.
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Indice

[modifica] Parametri

first, last -
iteratori forward che definiscono l'intervallo di esaminare
Original:
forward iterators defining the range to examine
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cmp - comparison function which returns ​true if if *a is less than *b.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
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 ForwardIterator.

[modifica] Valore di ritorno

una coppia costituita da un iteratore al più piccolo elemento come primo elemento ed un iteratore al più grande come il secondo elemento. Restituisce std::make_pair(first, first) se il campo è vuoto. Se alcuni elementi sono equivalenti al più piccolo elemento, l'iteratore al primo elemento tale viene restituito. Se diversi elementi sono equivalenti a l'elemento più grande, l'iteratore per l'ultimo elemento del genere viene restituito.
Original:
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.
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[modifica] Complessità

Alla maggior parte delle applicazioni max(floor(3/2(N−1)), 0) del predicato, in cui N = std::distance(first, last).
Original:
At most max(floor(3/2(N−1)), 0) applications of the predicate, where N = std::distance(first, last).
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[modifica] Possibile implementazione

First version
template<class ForwardIt>
std::pair<ForwardIt, ForwardIt> 
    minmax_element(ForwardIt first, ForwardIt last)
{
    typedef typename std::iterator_traits<ForwardIt>::value_type value_t;
    return std::minmax_element(first, last, std::less<value_t>());
}
Second version
template<class ForwardIt, class Compare>
std::pair<ForwardIt, ForwardIt> 
    minmax_element(ForwardIt first, ForwardIt last, Compare comp)
{
    std::pair<ForwardIt, ForwardIt> result(first, first);
 
    if (first == last) return result;
    if (++first == last) return result;
 
    if (comp(*first, *result.first)) {
        result.second = result.first;
        result.first = first;
    } else {
        result.second = first;
    }
    while (++first != last) {
        ForwardIt i = first;
        if (++first == last) {
            if (comp(*i, *result.first)) result.first = i;
            else if (!(comp(*i, *result.second))) result.second = i;
            break;
        } else {
            if (comp(*first, *i)) {
                if (comp(*first, *result.first)) result.first = first;
                if (!(comp(*i, *result.second))) result.second = i;
            } else {
                if (comp(*i, *result.first)) result.first = i;
                if (!(comp(*first, *result.second))) result.second = first;
            }
        }
    }
    return result;
}

[modifica] Esempio

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 };
 
    auto result = std::minmax_element(v.begin(), v.end());
    std::cout << "min element at: " << (result.first - v.begin()) << '\n';
    std::cout << "max element at: " << (result.second - v.begin()) << '\n';
}

Output:

min element at: 2
max element at: 6

[modifica] Vedi anche

restituisce l'elemento più piccolo in un intervallo
Original:
returns the smallest element in a range
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(funzione di modello) [edit]
restituisce l'elemento più grande in un intervallo
Original:
returns the largest element in a range
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(funzione di modello) [edit]