25 Algorithms library [algorithms]

25.7 Sorting and related operations [alg.sorting]

25.7.1 Sorting [alg.sort]

25.7.1.1 sort [sort]

template<class RandomAccessIterator> constexpr void sort(RandomAccessIterator first, RandomAccessIterator last); template<class ExecutionPolicy, class RandomAccessIterator> void sort(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> constexpr void sort(RandomAccessIterator first, RandomAccessIterator last, Compare comp); template<class ExecutionPolicy, class RandomAccessIterator, class Compare> void sort(ExecutionPolicy&& exec, RandomAccessIterator first, 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::sort(I first, S last, Comp comp = {}, Proj proj = {}); template<random_access_range R, class Comp = ranges::less, class Proj = identity> requires sortable<iterator_t<R>, Comp, Proj> constexpr safe_iterator_t<R> ranges::sort(R&& r, Comp comp = {}, Proj proj = {});
Let comp be less{} and proj be identity{} for the overloads with no parameters by those names.
Requires: For the overloads in namespace std, RandomAccessIterator shall meet the Cpp17ValueSwappable requirements ([swappable.requirements]) and the type of *first shall meet the Cpp17MoveConstructible (Table 26) and Cpp17MoveAssignable (Table 28) requirements.
Effects: Sorts the elements in the range [first, last) with respect to comp and proj.
Returns: last, for the overloads in namespace ranges.
Complexity: Let N be last - first.
comparisons and projections.

25.7.1.2 stable_­sort [stable.sort]

template<class RandomAccessIterator> void stable_sort(RandomAccessIterator first, RandomAccessIterator last); template<class ExecutionPolicy, class RandomAccessIterator> void stable_sort(ExecutionPolicy&& exec, RandomAccessIterator first, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> void stable_sort(RandomAccessIterator first, RandomAccessIterator last, Compare comp); template<class ExecutionPolicy, class RandomAccessIterator, class Compare> void stable_sort(ExecutionPolicy&& exec, RandomAccessIterator first, 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> I ranges::stable_sort(I first, S last, Comp comp = {}, Proj proj = {}); template<random_access_range R, class Comp = ranges::less, class Proj = identity> requires sortable<iterator_t<R>, Comp, Proj> safe_iterator_t<R> ranges::stable_sort(R&& r, Comp comp = {}, Proj proj = {});
Let comp be less{} and proj be identity{} for the overloads with no parameters by those names.
Requires: For the overloads in namespace std, RandomAccessIterator shall meet the Cpp17ValueSwappable requirements ([swappable.requirements]) and the type of *first shall meet the Cpp17MoveConstructible (Table 26) and Cpp17MoveAssignable (Table 28) requirements.
Effects: Sorts the elements in the range [first, last) with respect to comp and proj.
Returns: last for the overloads in namespace ranges.
Complexity: Let N be last - first.
If enough extra memory is available, comparisons.
Otherwise, at most comparisons.
In either case, twice as many projections as the number of comparisons.
Remarks: Stable ([algorithm.stable]).

25.7.1.3 partial_­sort [partial.sort]

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 = {});
Let comp be less{} and proj be identity{} for the overloads with no parameters by those names.
Requires: [first, middle) and [middle, last) shall be valid ranges.
For the overloads in namespace std, RandomAccessIterator shall meet the Cpp17ValueSwappable requirements ([swappable.requirements]) and the type of *first shall meet the Cpp17MoveConstructible (Table 26) and Cpp17MoveAssignable (Table 28) requirements.
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.
Returns: last for the overload in namespace ranges.
Complexity: Approximately (last - first) * log(middle - first) comparisons, and twice as many projections.
template<random_access_range R, class Comp = ranges::less, class Proj = identity> requires sortable<iterator_t<R>, Comp, Proj> constexpr safe_iterator_t<R> ranges::partial_sort(R&& r, iterator_t<R> middle, Comp comp = {}, Proj proj = {});
Effects: Equivalent to:
return ranges::partial_sort(ranges::begin(r), middle, ranges::end(r), comp, proj);

25.7.1.4 partial_­sort_­copy [partial.sort.copy]

template<class InputIterator, class RandomAccessIterator> constexpr RandomAccessIterator partial_sort_copy(InputIterator first, InputIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last); template<class ExecutionPolicy, class ForwardIterator, class RandomAccessIterator> RandomAccessIterator partial_sort_copy(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last); template<class InputIterator, class RandomAccessIterator, class Compare> constexpr RandomAccessIterator partial_sort_copy(InputIterator first, InputIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last, Compare comp); template<class ExecutionPolicy, class ForwardIterator, class RandomAccessIterator, class Compare> RandomAccessIterator partial_sort_copy(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, RandomAccessIterator result_first, RandomAccessIterator result_last, Compare comp); template<input_iterator I1, sentinel_for<I1> S1, random_access_iterator I2, sentinel_for<I2> S2, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires indirectly_copyable<I1, I2> && sortable<I2, Comp, Proj2> && indirect_strict_weak_order<Comp, projected<I1, Proj1>, projected<I2, Proj2>> constexpr ranges::partial_sort_copy_result<I1, I2> ranges::partial_sort_copy(I1 first, S1 last, I2 result_first, S2 result_last, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<input_range R1, random_access_range R2, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires indirectly_copyable<iterator_t<R1>, iterator_t<R2>> && sortable<iterator_t<R2>, Comp, Proj2> && indirect_strict_weak_order<Comp, projected<iterator_t<R1>, Proj1>, projected<iterator_t<R2>, Proj2>> constexpr ranges::partial_sort_copy_result<safe_iterator_t<R1>, safe_iterator_t<R2>> ranges::partial_sort_copy(R1&& r, R2&& result_r, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
Let N be .
Let comp be less{}, and proj1 and proj2 be identity{} for the overloads with no parameters by those names.
Requires: For the overloads in namespace std, RandomAccessIterator shall meet the Cpp17ValueSwappable requirements ([swappable.requirements]), the type of *result_­first shall meet the Cpp17MoveConstructible (Table 26) and Cpp17MoveAssignable (Table 28) requirements, and the expression *first shall be writable ([iterator.requirements.general]) to result_­first.
Expects: For iterators a1 and b1 in [first, last), and iterators x2 and y2 in [result_­first, result_­last), after evaluating the assignment *y2 = *b1, let E be the value of
bool(invoke(comp, invoke(proj1, *a1), invoke(proj2, *y2))).
Then, after evaluating the assignment *x2 = *a1, E is equal to
bool(invoke(comp, invoke(proj2, *x2), invoke(proj2, *y2))).
Note
: Writing a value from the input range into the output range does not affect how it is ordered by comp and proj1 or proj2. — end note
 ]
Effects: Places the first N elements as sorted with respect to comp and proj2 into the range [result_­first, result_­first + N).
Returns:
  • result_­first + N for the overloads in namespace std, or
  • {last, result_­first + N} for the overloads in namespace ranges.
Complexity: Approximately (last - first) * log N comparisons, and twice as many projections.

25.7.1.5 is_­sorted [is.sorted]

template<class ForwardIterator> constexpr bool is_sorted(ForwardIterator first, ForwardIterator last);
Effects: Equivalent to: return is_­sorted_­until(first, last) == last;
template<class ExecutionPolicy, class ForwardIterator> bool is_sorted(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last);
Effects: Equivalent to:
return is_sorted_until(std::forward<ExecutionPolicy>(exec), first, last) == last;
template<class ForwardIterator, class Compare> constexpr bool is_sorted(ForwardIterator first, ForwardIterator last, Compare comp);
Effects: Equivalent to: return is_­sorted_­until(first, last, comp) == last;
template<class ExecutionPolicy, class ForwardIterator, class Compare> bool is_sorted(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Compare comp);
Effects: Equivalent to:
return is_sorted_until(std::forward<ExecutionPolicy>(exec), first, last, comp) == last;
template<forward_iterator I, sentinel_for<I> S, class Proj = identity, indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less> constexpr bool ranges::is_sorted(I first, S last, Comp comp = {}, Proj proj = {}); template<forward_range R, class Proj = identity, indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less> constexpr bool ranges::is_sorted(R&& r, Comp comp = {}, Proj proj = {});
Effects: Equivalent to: return ranges​::​is_­sorted_­until(first, last, comp, proj) == last;
template<class ForwardIterator> constexpr ForwardIterator is_sorted_until(ForwardIterator first, ForwardIterator last); template<class ExecutionPolicy, class ForwardIterator> ForwardIterator is_sorted_until(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last); template<class ForwardIterator, class Compare> constexpr ForwardIterator is_sorted_until(ForwardIterator first, ForwardIterator last, Compare comp); template<class ExecutionPolicy, class ForwardIterator, class Compare> ForwardIterator is_sorted_until(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Compare comp); template<forward_iterator I, sentinel_for<I> S, class Proj = identity, indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less> constexpr I ranges::is_sorted_until(I first, S last, Comp comp = {}, Proj proj = {}); template<forward_range R, class Proj = identity, indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less> constexpr safe_iterator_t<R> ranges::is_sorted_until(R&& r, Comp comp = {}, Proj proj = {});
Let comp be less{} and proj be identity{} for the overloads with no parameters by those names.
Returns: The last iterator i in [first, last] for which the range [first, i) is sorted with respect to comp and proj.
Complexity: Linear.