std::min_element

Defined in header `<algorithm>`
	(1)
template< class ForwardIt > ForwardIt min_element( ForwardIt first, ForwardIt last );		(until C++17)
template< class ForwardIt > constexpr ForwardIt min_element( ForwardIt first, ForwardIt last );		(since C++17)
		(2)
template< class ForwardIt, class Compare > ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );			(until C++17)
template< class ForwardIt, class Compare > constexpr ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );			(since C++17)

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

Parameters

first, last	-	forward iterators defining the range to examine
cmp	-	comparison function object (i.e. an object that satisfies the requirements of `Compare`) which returns `true` 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 object 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`.

Return value

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

Complexity

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

Possible implementation

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

First version

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

Second version

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

Example

#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, 1, 4, 1, 5, 9};
 
    std::vector<int>::iterator result = std::min_element(std::begin(v), std::end(v));
    std::cout << "min element at: " << std::distance(std::begin(v), result);
}

Output:

min element at: 1

max_element	returns the largest element in a range (function template)
minmax_element (C++11)	returns the smallest and the largest element in a range (function template)
min	returns the smaller of the given values (function template)
std::experimental::parallel::min_element (parallelism TS)	parallelized version of `std::min_element` (function template)

Links:

http://en.cppreference.com/w/cpp/algorithm/min_element

doc_CPP

2016-10-11 10:04:51

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