# C++ Algorithm Library - is_heap() Function

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## Description

The C++ function std::algorithm::is_heap() tests whether given sequence is max heap or not. It uses operator< for comparison.

## Declaration

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

### C++11

```template <class RandomAccessIterator>
bool is_heap(RandomAccessIterator first, RandomAccessIterator last);
```

## Parameters

• first − Random access iterator to the initial position.

• last − Random access iterator to the final position.

## Return value

Returns true if given sequence is max heap otherwise returns false.

## Exceptions

Throws exception if either the element comparison or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Linear.

## Example

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

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

using namespace std;

int main(void) {
vector<int> v = {3, 5, 2, 1, 4};
bool result;

result = is_heap(v.begin(), v.end());

if (result == false)
cout << "Given sequence is not a max heap." << endl;

v = {5, 4, 3, 2, 1};

result = is_heap(v.begin(), v.end());

if (result == true)
cout << "Given sequence is a max heap." << endl;
}
```

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

```Given sequence is not a max heap.
Given sequence is a max heap.
```
algorithm.htm