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std::equal_range

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C++
 
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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binary_search
equal_range
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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Operazioni numeriche
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Numeric operations
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Libreria C
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C library
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Elemento definito nell'header <algorithm>
template< class ForwardIt, class T >

std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,

                 const T& value );
 (1)
template< class ForwardIt, class T, class Compare >

std::pair<ForwardIt,ForwardIt>
    equal_range( ForwardIt first, ForwardIt last,

                 const T& value, Compare comp );
 (2)
Restituisce un intervallo contenente tutti gli elementi uguali a value nel [first, last) campo ordinato. L'intervallo è definito da due iteratori, uno punta al primo elemento' non inferiore value e un'altra punta al primo elemento' superiori rispetto value. L'iteratore prima può essere alternativamente ottenuto con lower_bound(), il secondo - con upper_bound().
Original:
Returns a range containing all elements equal to value in the sorted range [first, last). The range is defined by two iterators, one pointing to the first element that is not less than value and another pointing to the first element greater than value. The first iterator may be alternatively obtained with lower_bound(), the second - with upper_bound().
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La prima versione utilizza operator< di confrontare gli elementi, la seconda versione utilizza la funzione di confronto dato comp.
Original:
The first version uses operator< to compare the elements, the second version uses the given comparison function comp.
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Indice

[modifica] Parametri

first, last -
la gamma di elementi da esaminare
Original:
the range of elements to examine
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value -
valore per confrontare gli elementi
Original:
value to compare the elements to
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comp - comparison function 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);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type1 must be such that an object of type T can be implicitly converted to Type1. The type Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to Type2. ​

Type requirements
-
ForwardIt must meet the requirements of ForwardIterator.

[modifica] Valore di ritorno

std::pair contenente una coppia di iteratori definiscono l'intervallo desiderato, il primo punta al primo elemento' non inferiore value e la seconda punta al primo elemento' maggiore rispetto value.
Original:
std::pair containing a pair of iterators defining the wanted range, the first pointing to the first element that is not less than value and the second pointing to the first element greater than value.
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Se non vi sono elementi' non meno di value, last viene restituito come primo elemento. Allo stesso modo se non ci sono elementi superiore di value, last viene restituito come il secondo elemento
Original:
If there are no elements not less than value, last is returned as the first element. Similarly if there are no elements greater than value, last is returned as the second element
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[modifica] Complessità

Logaritmica della distanza tra first e last
Original:
Logarithmic in the distance between first and last
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[modifica] Possibile implementazione

First version 
template<class ForwardIt, class T 
std::pair<ForwardIt,ForwardIt> 
    equal_range(ForwardIt first, ForwardIt last,
                const T& value)
{
    return std::make_pair(std::lower_bound(first, last, value),
                          std::upper_bound(first, last, value));
}
Second version 
template<class ForwardIt, class T, class Compare>
std::pair<ForwardIt,ForwardIt> 
    equal_range(ForwardIt first, ForwardIt last,
                const T& value, Compare comp);
{
    return std::make_pair(std::lower_bound(first, last, value, comp),
                          std::upper_bound(first, last, value, comp));
}

[modifica] Esempio

#include <algorithm>
#include <vector>
#include <iostream>
 
struct S
{
    int number;
    char name;
 
    S ( int number, char name  )
        : number ( number ), name ( name )
    {}
 
    // only the number is relevant with this comparison
    bool operator< ( const S& s ) const
    {
        return number < s.number;
    }
};
 
 
int main()
{
    std::vector<S> vec = { {1,'A'}, {2,'B'}, {2,'C'}, {2,'D'}, {3,'F'}, {4,'G'} };
 
    S value ( 2, '?' );
 
    auto p = std::equal_range(vec.begin(),vec.end(),value);
 
    for ( auto i = p.first; i != p.second; ++i )
        std::cout << i->name << ' ';
}

Output: 

B C D

[modifica] Vedi anche
restituisce un iteratore al primo elemento' non inferiore al valore dato
Original:
returns an iterator to the first element not less than the given value
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(funzione di modello) [modifica]
ritorna un iteratore al primo elemento' maggiore di un certo valore
Original:
returns an iterator to the first element greater than a certain value
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(funzione di modello) [modifica]
determina se un elemento è presente in un certo intervallo
Original:
determines if an element exists in a certain range
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(funzione di modello) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/algorithm/equal_range&oldid=24932"