# C++ Algorithm Library - adjacent_find() Function

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## Description

The C++ function std::algorithm::adjacent_find() finds the first occurrence of two consecutive elements that are identical and returns an iterator pointing to the first element if identical element exists consecutively otherwise returns an iterator pointing to the last element.

## Declaration

Following is the declaration for std::algorithm::adjacent_find() function form std::algorithm header.

```template <class ForwardIterator, class BinaryPredicate>
ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last, BinaryPredicate pred);
```

## Parameters

• first − Forward iterators to the initial positions of the searched sequence.

• last − Forward iterators to the final positions of the searched sequence.

• pred − This is function which takes two argument and returns bool.

## Return value

Returns an iterator pointing to the first element if identical element exists consecutively otherwise returns an iterator pointing to the last element.

## Exceptions

Exception is thrown if any element comparison object throws exception.

Please note that invalid arguments cause undefined behavior.

## Time complexity

Linear in the distance between first and last.

## Example

The following example shows the usage of std::algorithm::adjacent_find() function.

```#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool predicate(int a, int b) {
return (a == b);
}

int main(void) {
vector<int> v = {1, 2, 3, 3, 4, 5, 5};
auto it = adjacent_find(v.begin(), v.end());

if (it != v.end())
cout << "First occurrence of consecutive identical element = "
<< *it << endl;

it = adjacent_find(++it, v.end(), predicate);

if (it != v.end())
cout << "Second occurrence of consecutive identical element = "
<< *it << endl;

return 0;
}
```

Let us compile and run the above program, this will produce the following result −

```First occurrence of consecutive identical element = 3
Second occurrence of consecutive identical element = 5
```
algorithm.htm