25 Algorithms library [algorithms]

25.8 Sorting and related operations [alg.sorting]

25.8.1 Sorting [alg.sort]

25.8.1.3 partial_­sort [partial.sort]

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template<class RandomAccessIterator> constexpr void partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last); template<class ExecutionPolicy, class RandomAccessIterator> void partial_sort(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> constexpr void partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, Compare comp); template<class ExecutionPolicy, class RandomAccessIterator, class Compare> void partial_sort(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, Compare comp); template<random_­access_­iterator I, sentinel_­for<I> S, class Comp = ranges::less, class Proj = identity> requires sortable<I, Comp, Proj> constexpr I ranges::partial_sort(I first, I middle, S last, Comp comp = {}, Proj proj = {});
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Let comp be less{} and proj be identity{} for the overloads with no parameters by those names.
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Preconditions: [first, middle) and [middle, last) are valid ranges.
For the overloads in namespace std, RandomAccessIterator meets the Cpp17ValueSwappable requirements ([swappable.requirements]) and the type of *first meets the Cpp17MoveConstructible (Table 28) and Cpp17MoveAssignable (Table 30) requirements.
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Effects: Places the first middle - first elements from the range [first, last) as sorted with respect to comp and proj into the range [first, middle).
The rest of the elements in the range [middle, last) are placed in an unspecified order.
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Returns: last for the overload in namespace ranges.
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Complexity: Approximately (last - first) * log(middle - first) comparisons, and twice as many projections.
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template<random_­access_­range R, class Comp = ranges::less, class Proj = identity> requires sortable<iterator_t<R>, Comp, Proj> constexpr borrowed_iterator_t<R> ranges::partial_sort(R&& r, iterator_t<R> middle, Comp comp = {}, Proj proj = {});
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Effects: Equivalent to: 
return ranges::partial_sort(ranges::begin(r), middle, ranges::end(r), comp, proj);