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https://github.com/bolero-MURAKAMI/Sprout.git
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73 lines
2.7 KiB
C++
73 lines
2.7 KiB
C++
#ifndef SPROUT_DETAIL_ALGORITHM_COUNT_N_HPP
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#define SPROUT_DETAIL_ALGORITHM_COUNT_N_HPP
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#include <iterator>
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#include <type_traits>
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#include <sprout/config.hpp>
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#include <sprout/iterator/operation.hpp>
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#include <sprout/iterator/type_traits/is_iterator.hpp>
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#include <sprout/utility/pair.hpp>
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#include <sprout/algorithm/count.hpp>
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namespace sprout {
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namespace detail {
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template<typename RandomAccessIterator, typename T>
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inline SPROUT_CONSTEXPR typename std::enable_if<
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sprout::is_constant_distance_iterator<RandomAccessIterator>::value,
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typename std::iterator_traits<RandomAccessIterator>::difference_type
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>::type
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count_n(
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RandomAccessIterator first, typename std::iterator_traits<RandomAccessIterator>::difference_type n, T const& value,
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std::random_access_iterator_tag*
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)
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{
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return sprout::count(first, sprout::next(first, n), value);
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}
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template<typename InputIterator, typename T>
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inline SPROUT_CONSTEXPR sprout::pair<InputIterator, typename std::iterator_traits<InputIterator>::difference_type>
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count_n_impl(
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sprout::pair<InputIterator, typename std::iterator_traits<InputIterator>::difference_type> const& current,
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T const& value, typename std::iterator_traits<InputIterator>::difference_type n
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)
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{
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typedef sprout::pair<InputIterator, typename std::iterator_traits<InputIterator>::difference_type> type;
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return n == 1 ? type(sprout::next(current.first), current.second + (*current.first == value ? 1 : 0))
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: sprout::detail::count_n_impl(
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sprout::detail::count_n_impl(
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current,
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value, n / 2
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),
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value, n - n / 2
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)
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;
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}
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template<typename InputIterator, typename T>
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inline SPROUT_CONSTEXPR typename std::iterator_traits<InputIterator>::difference_type
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count_n(
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InputIterator first, typename std::iterator_traits<InputIterator>::difference_type n, T const& value,
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void*
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)
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{
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typedef sprout::pair<InputIterator, typename std::iterator_traits<InputIterator>::difference_type> type;
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return n == 0 ? 0
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: sprout::detail::count_n_impl(type(first, 0), value, n).second
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;
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}
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//
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// count_n
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//
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// recursion depth:
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// O(log N)
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//
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template<typename InputIterator, typename T>
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inline SPROUT_CONSTEXPR typename std::iterator_traits<InputIterator>::difference_type
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count_n(InputIterator first, typename std::iterator_traits<InputIterator>::difference_type n, T const& value) {
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typedef typename std::iterator_traits<InputIterator>::iterator_category* category;
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return sprout::detail::count_n(first, n, value, category());
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}
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} // namespace detail
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} // namespace sprout
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#endif // #ifndef SPROUT_DETAIL_ALGORITHM_COUNT_N_HPP
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