std::max_element - cppreference.com

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Elemento definito nell'header `<algorithm>`

`template< class ForwardIt > ForwardIt max_element( ForwardIt first, ForwardIt last );`	(1)

`template< class ForwardIt, class Compare > ForwardIt max_element( ForwardIt first, ForwardIt last, Compare comp );`	(2)

Finds the greatest element in the range [first, last). The first version uses operator< to compare the values, the second version uses the given comparison function comp.

Parametri

first, last	-	iteratori forward che definiscono l'intervallo di esaminare Original: forward iterators defining the range to examine The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
cmp	-	comparison function which returns `true` if if `a` is less* than `*b`. 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 `ForwardIt` can be dereferenced and then implicitly converted to both of them.
Type requirements
-`ForwardIt` must meet the requirements of `ForwardIterator`.

Valore di ritorno

Iterator to the greatest element in the range [first, last). If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element. Returns last if the range is empty.

Complessità

Esattamente max(N-1,0) confronti, N = std::distance(first, last) dove.

Original:

Exactly max(N-1,0) comparisons, where N = std::distance(first, last).

The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.

Possibile implementazione

First version
template<class ForwardIt> ForwardIt max_element(ForwardIt first, ForwardIt last) { if (first == last) { return last; } ForwardIt largest = first; ++first; for (; first != last; ++first) { if (largest < first) { largest = first; } } return largest; }
Second version
template<class ForwardIt, class Compare> ForwardIt max_element(ForwardIt first, ForwardIt last, Compare comp) { if (first == last) { return last; } ForwardIt largest = first; ++first; for (; first != last; ++first) { if (comp(largest, first)) { largest = first; } } return largest; }

First version

template<class ForwardIt>
ForwardIt max_element(ForwardIt first, ForwardIt last)
{
    if (first == last) {
        return last;
    }
    ForwardIt largest = first;
    ++first;
    for (; first != last; ++first) {
        if (*largest < *first) {
            largest = first;
        }
    }
    return largest;
}

Second version

template<class ForwardIt, class Compare>
ForwardIt max_element(ForwardIt first, ForwardIt last, 
                            Compare comp)
{
    if (first == last) {
        return last;
    }
    ForwardIt largest = first;
    ++first;
    for (; first != last; ++first) {
        if (comp(*largest, *first)) {
            largest = first;
        }
    }
    return largest;
}

Esempio

#include <algorithm>
#include <iostream>
#include <vector>
#include <cmath>

static bool abs_compare(int a, int b)
{
    return (std::abs(a) < std::abs(b));
}

int main()
{
    std::vector<int> v{ 3, 1, -14, 1, 5, 9 }; 
    std::vector<int>::iterator result;

    result = std::max_element(v.begin(), v.end());
    std::cout << "max element at: " << std::distance(v.begin(), result) << '\n';

    result = std::max_element(v.begin(), v.end(), abs_compare);
    std::cout << "max element (absolute) at: " << std::distance(v.begin(), result);
}

Output:

max element at: 5
max element (absolute) at: 2

Vedi anche


min_element	restituisce l'elemento più piccolo in un intervallo Original: returns the smallest element in a range 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]

minmax_element (C++11)	restituisce l'elemento più piccolo e il più grande in un intervallo Original: returns the smallest and the largest element in a range 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]

max	restituisce il più grande dei due elementi Original: returns the larger of two 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]