# Heap using STL C++

Heap data structure can be implemented in a range using STL which allows faster input into heap and retrieval of a number always results in the largest number i.e. largest number of the remaining numbers is popped out each time. Other numbers of the heap are arranged depending upon the implementation.

Operations on heap :

1. make_heap() :- This function is used to convert a range in a container to a heap.

2. front() :- This function displays the first element of heap which is the maximum number.

```// C++ code to demonstrate the working of
// make_heap(), front()
#include<iostream>
#include<algorithm> // for heap operations
using namespace std;
int main()
{

// Initializing a vector
vector<int> v1 = {20, 30, 40, 25, 15};

// Converting vector into a heap
// using make_heap()
make_heap(v1.begin(), v1.end());

// Displaying the maximum element of heap
// using front()
cout << "The maximum element of heap is : ";
cout << v1.front() << endl;

return 0;
}
```

Output:

```The maximum element of heap is : 40
```

3. push_heap() :- This function is used to insert elements into heap. The size of the heap is increased by 1. New element is placed appropriately in the heap.

4. pop_heap() :- This function is used to delete the maximum element of the heap. The size of heap is decreased by 1. The heap elements are reorganised accordingly after this operation.

```// C++ code to demonstrate the working of
// push_heap() and pop_heap()
#include<iostream>
#include<algorithm> // for heap operations
using namespace std;
int main()
{

// Initializing a vector
vector<int> v1 = {20, 30, 40, 25, 15};

// Converting vector into a heap
// using make_heap()
make_heap(v1.begin(), v1.end());

// Displaying the maximum element of heap
// using front()
cout << "The maximum element of heap is : ";
cout << v1.front() << endl;

// using push_back() to enter element
// in vector
v1.push_back(50);

// using push_heap() to reorder elements
push_heap(v1.begin(), v1.end());

// Displaying the maximum element of heap
// using front()
cout << "The maximum element of heap after push is : ";
cout << v1.front() << endl;

// using pop_heap() to delete maximum element
pop_heap(v1.begin(), v1.end());

// Displaying the maximum element of heap
// using front()
cout << "The maximum element of heap after pop is : ";
cout << v1.front() << endl;

return 0;
}
```

Output:

```The maximum element of heap is : 40
The maximum element of heap after push is : 50
The maximum element of heap after pop is : 40
```

5. sort_heap() :- This function is used to sort the heap. After this operation, the container is no longer a heap.

```// C++ code to demonstrate the working of
// sort_heap()
#include<iostream>
#include<algorithm> // for heap operations
using namespace std;
int main()
{

// Initializing a vector
vector<int> v1 = {20, 30, 40, 25, 15};

// Converting vector into a heap
// using make_heap()
make_heap(v1.begin(), v1.end());

// Displaying heap elements
cout << "The heap elements are : ";
for (int &x : v1)
cout << x << " ";
cout << endl;

// sorting heap using sort_heap()
sort_heap(v1.begin(), v1.end());

// Displaying heap elements
cout << "The heap elements after sorting are : ";
for (int &x : v1)
cout << x << " ";

return 0;
}
```

Output:

```The heap elements are : 40 30 20 25 15
The heap elements after sorting are : 15 20 25 30 40
```

6. is_heap() :- This function is used to check whether the container is heap or not. Generally, in most implementations, the reverse sorted container is considered as heap. Returns true if container is heap else returns false.

6. is_heap_until() :- This function returns the iterator to the position till the container is the heap. Generally, in most implementations, the reverse sorted container is considered as heap.

```// C++ code to demonstrate the working of
// is_heap() and is_heap_until()
#include<iostream>
#include<algorithm> // for heap operations
using namespace std;
int main()
{

// Initializing a vector
vector<int> v1 = {40, 30, 25, 35, 15};

// Declaring heap iterator
vector<int>::iterator it1;

// Checking if container is heap
// using is_heap()
is_heap(v1.begin(), v1.end())?
cout << "The container is heap ":
cout << "The container is not heap";
cout << endl;

// using is_heap_until() to check position
// till which container is heap
auto it = is_heap_until(v1.begin(), v1.end());

// Displaying heap range elements
cout << "The heap elements in container are : ";
for (it1=v1.begin(); it1!=it; it1++)
cout << *it1 << " ";

return 0;
}
```

Output:

```The container is not heap
The heap elements in container are : 40 30 25
```

This article is contributed by Manjeet Singh .If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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