std::partial_sum
De cppreference.com
<metanoindex/>
<tbody> </tbody>| Definido no cabeçalho <numeric>
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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) | |
Calcula as somas parciais dos elementos no subranges do
[first, last) alcance e grava-los para o início escala em d_first. A primeira versão utiliza operator+ para resumir os elementos, a segunda versão utiliza a função binária dada 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.The text has been machine-translated via Google Translate.
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Operação equivalente:
Original:
Equivalent operation:
The text has been machine-translated via Google Translate.
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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);
...
Parâmetros
| first, last | - | a gama de elementos a soma
Original: the range of elements to sum The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| d_first | - | o início do intervalo de destino
Original: the beginning of the destination range The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| op | - | binary operation function object that will be applied. The signature of the function should be equivalent to the following:
The signature does not need to have |
| Type requirements | ||
-InputIt must meet the requirements of InputIterator.
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-OutputIt must meet the requirements of OutputIterator.
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Valor de retorno
Iterador para o elemento passado o último elemento escrito.
Original:
Iterator to the element past the last element written.
The text has been machine-translated via Google Translate.
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Complexidade
Exatamente
(last - first) - 1 aplicações da operação bináriaOriginal:
Exactly
(last - first) - 1 applications of the binary operationThe text has been machine-translated via Google Translate.
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Possível implementação
| 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>());
}
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| 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;
}
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Exemplo
#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';
}
Saída:
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