23 Algorithms library [algorithms]

23.7 Sorting and related operations [alg.sorting]

23.7.2 Nth element [alg.nth.element]

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template<class RandomAccessIterator> constexpr void nth_element(RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last); template<class ExecutionPolicy, class RandomAccessIterator> void nth_element(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> constexpr void nth_element(RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last, Compare comp); template<class ExecutionPolicy, class RandomAccessIterator, class Compare> void nth_element(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last, Compare comp);
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Requires: RandomAccessIterator shall satisfy the Cpp17ValueSwappable requirements ([swappable.requirements]).
The type of *first shall satisfy the Cpp17MoveConstructible (Table 25) and Cpp17MoveAssignable (Table 27) requirements.
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Effects: After nth_­element the element in the position pointed to by nth is the element that would be in that position if the whole range were sorted, unless nth == last.
Also for every iterator i in the range [first, nth) and every iterator j in the range [nth, last) it holds that: !(*j < *i) or comp(*j, *i) == false.
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Complexity: For the overloads with no ExecutionPolicy, linear on average.
For the overloads with an ExecutionPolicy, applications of the predicate, and swaps, where .