25 Algorithms library [algorithms]

25.8 Sorting and related operations [alg.sorting]

25.8.3 Binary search [alg.binary.search]

25.8.3.3 equal_­range [equal.range]

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template<class ForwardIterator, class T> constexpr pair<ForwardIterator, ForwardIterator> equal_range(ForwardIterator first, ForwardIterator last, const T& value); template<class ForwardIterator, class T, class Compare> constexpr pair<ForwardIterator, ForwardIterator> equal_range(ForwardIterator first, ForwardIterator last, const T& value, Compare comp); template<forward_­iterator I, sentinel_­for<I> S, class T, class Proj = identity, indirect_­strict_­weak_­order<const T*, projected<I, Proj>> Comp = ranges::less> constexpr subrange<I> ranges::equal_range(I first, S last, const T& value, Comp comp = {}, Proj proj = {}); template<forward_­range R, class T, class Proj = identity, indirect_­strict_­weak_­order<const T*, projected<iterator_t<R>, Proj>> Comp = ranges::less> constexpr borrowed_subrange_t<R> ranges::equal_range(R&& r, const T& value, Comp comp = {}, Proj proj = {});
1
#
Let comp be less{} and proj be identity{} for overloads with no parameters by those names.
2
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Preconditions: The elements e of [first, last) are partitioned with respect to the expressions bool(invoke(comp, invoke(proj, e), value)) and !bool(invoke(comp, value, invoke(proj, e))).
Also, for all elements e of [first, last), bool(comp(e, value)) implies !bool(comp(​value, e)) for the overloads in namespace std.
3
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Returns:
  • (3.1)
    For the overloads in namespace std: 
    {lower_bound(first, last, value, comp),
 upper_bound(first, last, value, comp)}
  • (3.2)
    For the overloads in namespace ranges: 
    {ranges::lower_bound(first, last, value, comp, proj),
 ranges::upper_bound(first, last, value, comp, proj)}
4
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Complexity: At most comparisons and projections.