Namespace
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std::partition

Da cppreference.com.
< cpp‎ | algorithm

 
 
Algoritmo libreria
Funzioni
Original:
Functions
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Non modifica le operazioni di sequenza
Original:
Non-modifying sequence operations
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Modifica delle operazioni di sequenza
Original:
Modifying sequence operations
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Partizionamento operazioni
Original:
Partitioning operations
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is_partitioned(C++11)
partition
partition_copy(C++11)
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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Impostare le operazioni (su intervalli ordinati)
Original:
Set operations (on sorted ranges)
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Heap operazioni
Original:
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
Original:
C library
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Defined in header <algorithm>
template< class BidirIt, class UnaryPredicate >

BidirectionalIterator partition( BidirIt first, BidirIt last,
                                 UnaryPredicate p );
template< class ForwardIt, class UnaryPredicate >
ForwardIt partition( ForwardIt first, ForwardIt last,

                     UnaryPredicate p );
(C fino + 11)

(dal C++11)
Riordina gli elementi nel [first, last) gamma in modo tale che tutti gli elementi per cui il predicato p rendimenti true precedere gli elementi per i quali predicato p rendimenti false. Ordine relativo degli elementi non è conservato.
Original:
Reorders the elements in the range [first, last) in such a way that all elements for which the predicate p returns true precede the elements for which predicate p returns false. Relative order of the elements is not preserved.
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Indice

[modifica] Parametri

first, last -
la gamma di elementi da riordinare
Original:
the range of elements to reorder
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p - unary predicate which returns ​true
se l'elemento deve essere ordinato prima di altri elementi
Original:
if the element should be ordered before other elements
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.

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

 bool pred(const Type &a);

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

Type requirements
-
BidirIt must meet the requirements of BidirectionalIterator.
-
ForwardIt must meet the requirements of ValueSwappable and ForwardIterator. However, the operation is more efficient if ForwardIt also satisfies the requirements of BidirectionalIterator

[modifica] Valore di ritorno

Iteratore al primo elemento del secondo gruppo.
Original:
Iterator to the first element of the second group.
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[modifica] Complessità

Esattamente last-first applicazioni del predicato e la maggior parte delle operazioni di swap last-first. Se ForwardIt soddisfa i requisiti della maggior parte delle operazioni di swap in BidirectionalIterator (last-first)/2 sono fatte.
Original:
Exactly last-first applications of the predicate and at most last-first swaps. If ForwardIt meets the requirements of BidirectionalIterator at most (last-first)/2 swaps are done.
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[modifica] Possibile implementazione

template<class BidirIt, class UnaryPredicate>
BidirIt partition(BidirIt first, BidirIt last, UnaryPredicate p)
{
    while (1) {
        while ((first != last) && p(*first)) {
            ++first;
        }
        if (first == last--) break;
        while ((first != last) && !p(*last)) {
            --last;
        }
        if (first == last) break;
        std::swap(*first++, *last);
    }
    return first;
}

[modifica] Esempio

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
 
bool is_even(int i) { return i % 2 == 0; }
 
int main()
{
    std::vector<int> v;
    for (int i = 0; i < 10; ++i) v.push_back(i);
 
    std::cout << "Original vector:\n    ";
    std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
 
    // Partition the vector
    std::vector<int>::iterator p =
        std::partition(v.begin(), v.end(), std::ptr_fun(is_even));
 
    std::cout << "\nPartitioned vector:\n    ";
    std::copy(v.begin(), v.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\nBefore partition:\n    ";
    std::copy(v.begin(), p,       std::ostream_iterator<int>(std::cout, " "));
    std::cout << "\nAfter partition:\n    ";
    std::copy(p,         v.end(), std::ostream_iterator<int>(std::cout, " "));
}

Possible output:

Original vector:
    0 1 2 3 4 5 6 7 8 9 
Partitioned vector:
    0 8 2 6 4 5 3 7 1 9 
Before partition:
    0 8 2 6 4 
After partition:
    5 3 7 1 9

[modifica] Vedi anche

determina se il campo è diviso dal predicato specificato
Original:
determines if the range is partitioned by the given predicate
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(funzione di modello) [edit]
divide gli elementi in due gruppi, mantenendo l'ordine relativo
Original:
divides elements into two groups while preserving their relative order
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(funzione di modello) [edit]