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std::set_intersection - cppreference.com

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Elemento definito nell'header

<algorithm>

template< class InputIt1, class InputIt2, class OutputIt > OutputIt set_intersection( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first );

 (1)

template< class InputIt1, class InputIt2, class OutputIt, class Compare > OutputIt set_intersection( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, OutputIt d_first, Compare comp );

 (2)

Costruisce un inizio gamma smistati d_first costituito da elementi che si trovano in entrambe le gamme filtrate [first1, last1) e [first2, last2). La prima versione si aspetta che sia l'ingresso che varia da ordinare con operator<, la seconda versione si aspetta che essere ordinati con il confronto comp data funzione. Se qualche elemento si trova m volte in [first1, last1) e n volte [first2, last2), gli elementi std::min(m, n) primo verranno copiati dalla prima serie alla gamma di destinazione. L'ordine degli elementi equivalenti è conservato. L'intervallo risultante non possono sovrapporsi uno dei campi di ingresso.

Original:

Constructs a sorted range beginning at d_first consisting of elements that are found in both sorted ranges [first1, last1) and [first2, last2). The first version expects both input ranges to be sorted with operator<, the second version expects them to be sorted with the given comparison function comp. If some element is found m times in [first1, last1) and n times in [first2, last2), the first std::min(m, n) elements will be copied from the first range to the destination range. The order of equivalent elements is preserved. The resulting range cannot overlap with either of the input ranges.

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Parametri

first1, last1 -

la prima gamma di elementi da esaminare

Original:

the first range of elements to examine

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first2, last2 -

il secondo intervallo di elementi da esaminare

Original:

the second range of elements to examine

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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 types Type1 and Type2 must be such that objects of types InputIt1 and InputIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. ​

Type requirements
-InputIt1 must meet the requirements of InputIterator.
-InputIt2 must meet the requirements of InputIterator.
-OutputIt must meet the requirements of OutputIterator.

Valore di ritorno

Iterator oltre la fine della gamma costruito.

Original:

Iterator past the end of the constructed range.

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Complessità

A confronto la maggior parte 2·(N1+N2-1), dove N1 = std::distance(first1, last1) e N2 = std::distance(first2, last2).

Original:

At most 2·(N1+N2-1) comparisons, where N1 = std::distance(first1, last1) and N2 = std::distance(first2, last2).

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Possibile implementazione

First version 
template<class InputIt1, class InputIt2, class OutputIt>
OutputIt set_intersection(InputIt1 first1, InputIt1 last1,
                          InputIt2 first2, InputIt2 last2,
                          OutputIt d_first)
{
    while (first1 != last1 && first2 != last2) {
        if (*first1 < *first2) {
            ++first1;
        } else  {
            if (!(*first2 < *first1)) {
                *d_first++ = *first1++;
            }
            ++first2;
        }
    }
    return d_first;
}
Second version 
template<class InputIt1, class InputIt2,
         class OutputIt, class Compare>
OutputIt set_intersection(InputIt1 first1, InputIt1 last1,
                          InputIt2 first2, InputIt2 last2,
                          OutputIt d_first, Compare comp)
{
    while (first1 != last1 && first2 != last2) {
        if (comp(*first1, *first2)) {
            ++first1;
        } else {
            if (!comp(*first2, *first1)) {
                *d_first++ = *first1++;
            }
            ++first2;
        }
    }
    return d_first;
}

Esempio

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
int main()
{
    std::vector<int> v1{1,2,3,4,5,6,7,8};
    std::vector<int> v2{        5,  7,  9,10};
    std::sort(v1.begin(), v1.end());
    std::sort(v2.begin(), v2.end());

    std::vector<int> v_intersection;

    std::set_intersection(v1.begin(), v1.end(),
                          v2.begin(), v2.end(),
                          std::back_inserter(v_intersection));
    for(int n : v_intersection)
        std::cout << n << ' ';
}

Output:

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