count_if.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2020 Tobias Hienzsch
 
#ifndef TETL_ALGORITHM_COUNT_IF_HPP
#define TETL_ALGORITHM_COUNT_IF_HPP
 
#include <etl/_iterator/iterator_traits.hpp>
 
namespace etl {
 
/// Returns the number of elements in the range `[first, last)`
/// satisfying specific criteria. Counts elements for which predicate p returns
/// true.
///
/// \param first The range of elements to examine.
/// \param last The range of elements to examine.
/// \param p Unary predicate which returns ​true for the required elements.
///
/// https://en.cppreference.com/w/cpp/algorithm/count
///
/// \ingroup algorithm
template <typename InputIt, typename Predicate>
[[nodiscard]] constexpr auto count_if(InputIt first, InputIt last, Predicate p) ->
    typename iterator_traits<InputIt>::difference_type
{
    auto result = typename etl::iterator_traits<InputIt>::difference_type{0};
    for (; first != last; ++first) {
        if (p(*first)) {
            ++result;
        }
    }
    return result;
}
 
} // namespace etl
 
#endif // TETL_ALGORITHM_COUNT_IF_HPP