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

The C++ algorithm::make_heap function is used to rearrange the elements in the range [first,last) in such a way that they form a max heap.

### Syntax

```//default version
template <class RandomAccessIterator>
void make_heap(
RandomAccessIterator first,
RandomAccessIterator last
);

//custom version
template <class RandomAccessIterator, class Compare>
void make_heap(
RandomAccessIterator first,
RandomAccessIterator last,
BinaryPredicate 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. It follows the strict weak ordering to order the elements.

None.

### Time Complexity

Up to linear in three times the distance between first and last i.e, Θ(3n), where n is the distance between first and last.

### Example:

In the example below, the algorithm::make_heap function is used to rearrange the elements of a given vector to form a max heap.

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

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

cout<<"\nAfter make_heap call, vec contains:";
for(it = vec.begin(); it != vec.end(); ++it)
cout<<" "<<*it;

return 0;
}
```

The output of the above code will be:

```vec contains: 10 5 55 22 27 -10
After make_heap call, vec contains: 55 27 10 22 5 -10
```

❮ C++ <algorithm> Library

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