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std::random_shuffle, std::shuffle

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< 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
Original:
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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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 RandomIt >
void random_shuffle( RandomIt first, RandomIt last );
(1)
template< class RandomIt, class RandomFunc >

void random_shuffle( RandomIt first, RandomIt last, RandomFunc& r );

template< class RandomIt, class RandomFunc >

void random_shuffle( RandomIt first, RandomIt last, RandomFunc&& r );
(2) (C fino + 11)



(dal C++11)
template< class RandomIt, class URNG >
void shuffle( RandomIt first, RandomIt last, URNG&& g );
(3) (dal C++11)
Riordina gli elementi nell'intervallo dato [first, last) tali che ogni permutazione possibile di tali elementi ha la stessa probabilità di apparizione.
Original:
Reorders the elements in the given range [first, last) such that each possible permutation of those elements has equal probability of appearance.
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1)
Il generatore di numeri casuali è l'implementazione definita, ma la std::rand funzione viene spesso utilizzata.
Original:
The random number generator is implementation-defined, but the function std::rand is often used.
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2)
Il generatore di numeri casuali è l'oggetto funzione r.
Original:
The random number generator is the function object r.
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3)
Il generatore di numeri casuali è l'oggetto funzione g.
Original:
The random number generator is the function object g.
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Indice

[modifica] Parametri

first, last -
la gamma di elementi per mescolare in modo casuale
Original:
the range of elements to shuffle randomly
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r -
oggetto funzione che restituisce un valore scelto a caso di tipo convertibile iterator_traits<RandomIt>::difference_type nell'intervallo [0, n) se invocato come r(n)
Original:
function object returning a randomly chosen value of type convertible to iterator_traits<RandomIt>::difference_type in the interval [0,n) if invoked as r(n)
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g -
oggetto funzione che restituisce un valore scelto a caso di URNG::result_type tipo nell'intervallo [g.min (), g.max ()] se invocato come g() (ad esempio, uno dei generatori di numeri casuali uniformi da <random>)
Original:
function object returning a randomly chosen value of type URNG::result_type in the interval [g.min(), g.max()] if invoked as g() (e.g. any of the uniform random number generators from <random>)
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Type requirements
-
RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
-
URNG must meet the requirements of UniformRandomNumberGenerator.

[modifica] Valore di ritorno

(Nessuno)
Original:
(none)
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[modifica] Complessità

lineare la distanza tra first e last
Original:
linear in the distance between first and last
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[modifica] Possibile implementazione

First version
template<class RandomIt, class RandomFunc>
void random_shuffle(RandomIt first, RandomIt last, RandomFunc&& r)
{
    typename std::iterator_traits<RandomIt>::difference_type i, n;
    n = last - first;
    for (i = n-1; i > 0; --i) {
        using std::swap;
        swap(first[i], first[r(i+1)]);
    }
}
Second version
template<class RandomIt, class UniformRandomNumberGenerator>
void shuffle(RandomIt first, RandomIt last, 
             UniformRandomNumberGenerator&& g)
{
    typedef typename std::iterator_traits<RandomIt>::difference_type diff_t;
    typedef typename std::make_unsigned<diff_t>::type udiff_t;
    typedef typename std::uniform_int_distribution<udiff_t> distr_t;
    typedef typename distr_t::param_type param_t;
 
    distr_t D;
    diff_t n = last - first;
    for (diff_t i = n-1; i > 0; --i) {
        using std::swap;
        swap(first[i], first[D(g, param_t(0, i))]);
    }
}

[modifica] Esempio

Il codice seguente mescola casualmente i numeri interi 1 .. 10:
Original:
The following code randomly shuffles the integers 1..10:
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#include <random>
#include <algorithm>
#include <iterator>
#include <iostream>
 
int main()
{
    std::vector<int> v = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
 
    std::random_device rd;
    std::mt19937 g(rd());
 
    std::shuffle(v.begin(), v.end(), g);
 
    copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\n";
}


Uscita possibile:
Original:
Possible output:
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8 6 10 4 2 3 7 1 9 5

[modifica] Vedi anche

generates the next greater lexicographic permutation of a range of elements
(funzione di modello) [edit]
generates the next smaller lexicographic permutation of a range of elements
(funzione di modello) [edit]