std::nth_element - cppreference.com

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Elemento definito nell'header `<algorithm>`

`template< class RandomIt > void nth_element( RandomIt first, RandomIt nth, RandomIt last );`	(1)

`template< class RandomIt, class Compare > void nth_element( RandomIt first, RandomIt nth, RandomIt last, Compare comp );`	(2)

Parzialmente ordina la [first, last) intervallo in ordine crescente in modo che tutti gli elementi della gamma [first, nth) sono meno rispetto a quelli del [nth, last) gamma. La prima versione utilizza operator< di confrontare gli elementi, la seconda versione utilizza la data comp funzione di confronto. L'elemento posto in posizione nth è esattamente l'elemento che si verificano in questa posizione se l'intervallo è stato completamente ordinato.

Original:

Partially sorts the range [first, last) in ascending order so that all elements in the range [first, nth) are less than those in the range [nth, last). The first version uses operator< to compare the elements, the second version uses the given comparison function comp. The element placed in the nth position is exactly the element that would occur in this position if the range was fully sorted.

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Parametri

first, last	-	iteratori ad accesso casuale che definiscono il tipo gamma Original: random access iterators defining the range sort The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
nth	-	iteratore ad accesso casuale la definizione del punto di partizione ordinamento Original: random access iterator defining the sort partition point The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
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 an object of type `RandomIt` can be dereferenced and then implicitly converted to both of them.
Type requirements
-`RandomIt` must meet the requirements of `ValueSwappable` and `RandomAccessIterator`.
-The type of dereferenced `RandomIt` must meet the requirements of `MoveAssignable` and `MoveConstructible`.

Valore di ritorno

(Nessuno)

Original:

(none)

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Complessità

Lineare in std::distance(first, last) in media.

Original:

Linear in std::distance(first, last) on average.

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Esempio

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>

int main()
{
    std::vector<int> v{5, 6, 4, 3, 2, 6, 7, 9, 3};

    std::nth_element(v.begin(), v.begin() + v.size()/2, v.end());
    std::cout << "The median is " << v[v.size()/2] << '\n';

    std::nth_element(v.begin(), v.begin()+1, v.end(), std::greater<int>());
    std::cout << "The second largest element is " << v[1] << '\n';
}

Output:

The median is 5
The second largest element is 7

Vedi anche


partial_sort_copy	copie e parzialmente ordina una serie di elementi Original: copies and partially sorts a range of elements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]

stable_sort	Ordina un intervallo di elementi, mantenendo ordine tra elementi uguali Original: sorts a range of elements while preserving order between equal elements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]

sort	ordina una serie in ordine crescente Original: sorts a range into ascending order The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (funzione di modello) [modifica]