std::equal_range - cppreference.com

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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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Parametri

first, last	-	la gamma di elementi da esaminare Original: the range of elements to examine The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
value	-	valore per confrontare gli elementi Original: value to compare the elements to The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
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`.

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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Complessità

Logaritmica della distanza tra first e last

Original:

Logarithmic in the distance between first and last

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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)); }

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));
}

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:

Vedi anche


lower_bound	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 The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]**

upper_bound	ritorna un iteratore al primo elemento' maggiore di un certo valore Original: *returns an iterator to the first element greater* than a certain value The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]**

binary_search	determina se un elemento è presente in un certo intervallo Original: determines if an element exists in a certain range The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]