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std::partial_sum

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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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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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adjacent_difference
partial_sum
Libreria C
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C library
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Elemento definito nell'header <numeric>
template< class InputIt, class OutputIt >
OutputIt partial_sum( InputIt first, InputIt last, OutputIt d_first );
 (1)
template< class InputIt, class OutputIt, class BinaryOperation >

OutputIt partial_sum( InputIt first, InputIt last, OutputIt d_first,

                      BinaryOperation op );
 (2)
Calcola le somme parziali degli elementi nel sottointervalli della [first, last) gamma e li scrive all'inizio gamma a d_first. La prima versione utilizza operator+ per riassumere gli elementi, la seconda versione utilizza la funzione binaria data op.
Original:
Computes the partial sums of the elements in the subranges of the range [first, last) and writes them to the range beginning at d_first. The first version uses operator+ to sum up the elements, the second version uses the given binary function op.
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Equivalente funzionamento:
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Equivalent operation:
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*(d_first)   = *first;
*(d_first+1) = *first + *(first+1);
*(d_first+2) = *first + *(first+1) + *(first+2);
*(d_first+3) = *first + *(first+1) + *(first+2) + *(first+3);
...

Indice

[modifica] Parametri

first, last -
l'intervallo di elementi di somma
Original:
the range of elements to sum
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d_first -
l'inizio del campo di destinazione
Original:
the beginning of the destination range
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op - binary operation function object that will be applied.

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

 Ret fun(const Type1 &a, const Type2 &b);

The signature does not need to have const &.
The type  Type1 must be such that an object of type iterator_traits<InputIt>::value_type can be implicitly converted to  Type1. The type  Type2 must be such that an object of type InputIt can be dereferenced and then implicitly converted to  Type2. The type  Ret must be such that an object of type iterator_traits<InputIt>::value_type can be assigned a value of type  Ret. ​

Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.

[modifica] Valore di ritorno

Iterator all'elemento passato l'ultimo elemento scritto.
Original:
Iterator to the element past the last element written.
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[modifica] Complessità

Esattamente (last - first) - 1 applicazioni della operazione binaria
Original:
Exactly (last - first) - 1 applications of the binary operation
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[modifica] Possibile implementazione

First version 
template<class InputIt, class OutputIt>
OutputIt partial_sum(InputIt first, InputIt last, 
                           OutputIt d_first)
{
    return std::partial_sum(first, last, d_first, 
                            std::plus<InputIt, InputIt>());
}
Second version 
template<class InputIt, class OutputIt, class BinaryOperator>
OutputIt partial_sum(InputIt first, InputIt last, 
                           OutputIt d_first, BinaryOperation op)
{
    if (first == last) return d_first;
 
    typename std::iterator_traits<InputIt>::value_type sum = *first;
    *d_first = sum;
 
    while (++first != last) {
       sum = op(sum, *first);
       *++d_first = sum;
    }
    return ++d_first;
}

[modifica] Esempio

#include <numeric>
#include <vector>
#include <iostream>
#include <iterator>
#include <functional>
int main()
{
    std::vector<int> v = {2,2,2,2,2,2,2,2,2,2};
 
    std::cout << "The first 10 even numbers are: ";
    std::partial_sum(v.begin(), v.end(), 
                     std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
 
    std::partial_sum(v.begin(), v.end(), v.begin(), std::multiplies<int>());
    std::cout << "The first 10 powers of 2 are: ";
    for(auto n: v) {
        std::cout << n << " ";
    }
    std::cout << '\n';
}

Output: 

The first 10 even numbers are: 2 4 6 8 10 12 14 16 18 20 
The first 10 powers of 2 are: 2 4 8 16 32 64 128 256 512 1024

[modifica] Vedi anche
calcola le differenze tra elementi adiacenti in un intervallo
Original:
computes the differences between adjacent elements in a range
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(funzione di modello) [modifica]
riassume una serie di elementi
Original:
sums up a range of elements
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(funzione di modello) [modifica]
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/algorithm/partial_sum&oldid=24969"