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std::experimental::ranges::search_n - cppreference.com

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template< ForwardIterator I, Sentinel<I> S, class T,
          class Pred = ranges::equal_to<>, class Proj = ranges::identity >
    requires IndirectlyComparable<I, const T*, Pred, Proj>
I search_n( I first, S last, ranges::difference_type_t<I> count,
            const T& value, Pred pred = Pred{}, Proj proj = Proj{} );
(1) (ranges TS) 
template< ForwardRange R, class T, class Pred = ranges::equal_to<>,
          class Proj = ranges::identity >
    requires IndirectlyComparable<ranges::iterator_t<R>, const T*, Pred, Proj>
ranges::safe_iterator_t<R> search_n( R&& r, 
                                     ranges::difference_type_t<ranges::iterator_t<R>> count,
                                     const T& value, Pred pred = Pred{}, Proj proj = Proj{} );
(2) (ranges TS)

1) Searches the range [first, last) for the first sequence of count elements whose projected values are each equal to the given value value according to the predicate pred.

2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

Parameters

first, last - the range of elements to examine
r - the range of elements to examine
count - the length of the sequence to search for
value - the value to search for
pred - the predicate that compares the projected elements with value
proj - the projection to apply to the elements

Return value

Iterator to the beginning of the found sequence in the range [first, last). If no such sequence is found, an iterator that compares equal to last is returned.

Complexity

At most last - first applications of the predicate and the projection.

Possible implementation

template<ForwardIterator I, Sentinel<I> S, class T,
         class Pred = ranges::equal_to<>, class Proj = ranges::identity>
    requires IndirectlyComparable<I, const T*, Pred, Proj>
I search_n(I first, S last, ranges::difference_type_t<I> count,
           const T& value, Pred pred = Pred{}, Proj proj = Proj{})
{
    for (; first != last; ++first)
    {
        if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
            continue;

        I candidate = first;
        ranges::difference_type_t<I> cur_count = 0;

        while (true)
        {
            ++cur_count;
            if (cur_count == count)
                // success
                return candidate;

            ++first;
            if (first == last)
                // exhausted the list
                return first;

            if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
                // too few in a row
                break;
        }
    }
    return first;
}

Example

See also

searches for the first occurrence of a number consecutive copies of an element in a range
(function template & algorithm function object)[edit]
finds the last sequence of elements in a certain range
(function template) [edit]
finds the first element satisfying specific criteria
(function template) [edit]
searches for a range of elements
(function template) [edit]