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std::binary_search

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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
Original:
Partitioning operations
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Ordinamento delle operazioni (su intervalli ordinati)
Original:
Sorting operations (on sorted ranges)
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Binarie (le operazioni di ricerca sui campi ordinati)
Original:
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 >
bool binary_search( ForwardIt first, ForwardIt last, const T& value );
 (1)
template< class ForwardIt, class T, class Compare >
bool binary_search( ForwardIt first, ForwardIt last, const T& value, Compare comp );
 (2)
Controlla se il [first, last) gamma ordinato contiene un elemento uguale a value. La prima versione utilizza operator< di confrontare gli elementi, la seconda versione utilizza la funzione di confronto dato comp.
Original:
Checks if the sorted range [first, last) contains an element equal to value. 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

true se un elemento uguale a value si trova, false altrimenti.
Original:
true if an element equal to value is found, false otherwise.
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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>
bool binary_search(ForwardIt first, ForwardIt last, const T& value)
{
    first = std::lower_bound(first, last, value);
    return (first != last && !(value < *first));
}
Second version 
template<class ForwardIt, class T, class Compare>
bool binary_search(ForwardIt first, ForwardIt last, const T& value, Compare comp)
{
    first = std::lower_bound(first, last, value);
    return (first != last && !(comp(value, *first));
}

[modifica] Esempio

#include <iostream>
#include <algorithm>
#include <vector>
 
int main()
{
    std::vector<int> haystack {1, 3, 4, 5, 9};
    std::vector<int> needles {1, 2, 3};
 
    for (auto needle : needles) {
        std::cout << "Searching for " << needle << '\n';
        if (std::binary_search(haystack.begin(), haystack.end(), needle)) {
            std::cout << "Found " << needle << '\n';
        } else {
            std::cout << "no dice!\n";
        }
    }
}

Output: 

Searching for 1
Found 1
Searching for 2
no dice!
Searching for 3
Found 3

[modifica] Vedi anche
torna gamma di elementi che corrispondono un tasto specifico
Original:
returns range of elements matching a specific key
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(funzione di modello) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/algorithm/binary_search&oldid=24925"