# 27 Algorithms library [algorithms]

## 27.6 Non-modifying sequence operations [alg.nonmodifying]

### 27.6.10 Adjacent find [alg.adjacent.find]

```template<class ForwardIterator> constexpr ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last); template<class ExecutionPolicy, class ForwardIterator> ForwardIterator adjacent_find(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last); template<class ForwardIterator, class BinaryPredicate> constexpr ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last, BinaryPredicate pred); template<class ExecutionPolicy, class ForwardIterator, class BinaryPredicate> ForwardIterator adjacent_find(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, BinaryPredicate pred); template<forward_iterator I, sentinel_for<I> S, class Proj = identity, indirect_binary_predicate<projected<I, Proj>, projected<I, Proj>> Pred = ranges::equal_to> constexpr I ranges::adjacent_find(I first, S last, Pred pred = {}, Proj proj = {}); template<forward_range R, class Proj = identity, indirect_binary_predicate<projected<iterator_t<R>, Proj>, projected<iterator_t<R>, Proj>> Pred = ranges::equal_to> constexpr borrowed_iterator_t<R> ranges::adjacent_find(R&& r, Pred pred = {}, Proj proj = {}); ```
Let E be:
• *i == *(i + 1) for the overloads with no parameter pred;
• pred(*i, *(i + 1)) != false for the overloads with a parameter pred and no parameter proj;
• bool(invoke(pred, invoke(proj, *i), invoke(proj, *(i + 1)))) for the overloads with both parameters pred and proj.
Returns: The first iterator i such that both i and i + 1 are in the range [first, last) for which E holds.
Returns last if no such iterator is found.
Complexity: For the overloads with no ExecutionPolicy, exactly min((i - first) + 1,  (last - first) - 1) applications of the corresponding predicate, where i is adjacent_find's return value.
For the overloads with an ExecutionPolicy, applications of the corresponding predicate, and no more than twice as many applications of any projection.