# C++ <algorithm> - is_heap() Function

The C++ algorithm::is_heap function returns true if the range [first,last) forms a heap, as if constructed with make_heap.

The elements are compared using operator< (in first version) or comp (in second version).

### Syntax

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

//custom version
template <class RandomAccessIterator, class Compare>
bool is_heap (RandomAccessIterator first, RandomAccessIterator last,
Compare comp);
```

### Parameters

 `first` Specify initial position of the random-access iterator. The range used is [first,last). `last` Specify final position of the random-access iterator. The range used is [first,last). `comp` A binary predicate that takes two elements in the range as arguments and returns a bool. The returned value indicates whether the first argument is considered to go before the second using the strict weak ordering it defines.

### Return Value

Returns true if the range [first,last) is a heap (as if constructed with make_heap), false otherwise.

### Time Complexity

Up to linear the distance between first and last i.e, Θ(n), where n is the distance between first and last.

### Example:

In the example below, the algorithm::is_heap function is used to check a whether a given range of a vector forms a heap or not.

```#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main (){
vector<int> vec{10, 5, 55, 22, 27, -10};
vector<int>::iterator it;

cout<<boolalpha;
cout<<"vec contains:";
for(it = vec.begin(); it != vec.end(); ++it)
cout<<" "<<*it;

//checking for heap
cout<<"\nIs vec a heap: "<<
is_heap(vec.begin(), vec.end());

//make the vector a heap
make_heap(vec.begin(), vec.end());

cout<<"\n\nvec contains:";
for(it = vec.begin(); it != vec.end(); ++it)
cout<<" "<<*it;

//checking for heap
cout<<"\nIs vec a heap: "<<
is_heap(vec.begin(), vec.end());

return 0;
}
```

The output of the above code will be:

```vec contains: 10 5 55 22 27 -10
Is vec a heap: false

vec contains: 55 27 10 22 5 -10
Is vec a heap: true
```

❮ C++ <algorithm> Library

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