Heapify.cpp

// Heapify is the process of converting a binary tree into Heap data structure.
#include <iostream>

using namespace std;


void heapify(int arr[], int n, int i)
{
	int largest = i; // Initialize largest as root
	int l = 2 * i + 1; // left = 2*i + 1
	int r = 2 * i + 2; // right = 2*i + 2

	// If left child is larger than root
	if (l < n && arr[l] > arr[largest])
		largest = l;

	// If right child is larger than largest so far
	if (r < n && arr[r] > arr[largest])
		largest = r;

	// If largest is not root
	if (largest != i) {
		swap(arr[i], arr[largest]);

		// Recursively heapify the affected sub-tree
		heapify(arr, n, largest);
	}
}

// Function to build a Max-Heap from the given array
void buildHeap(int arr[], int n)
{
	// Index of last non-leaf node
	int startIdx = (n / 2) - 1;

	// Perform reverse level order traversal
	// from last non-leaf node and heapify
	// each node
	for (int i = startIdx; i >= 0; i--) {
		heapify(arr, n, i);
	}
}

// A utility function to print the array
// representation of Heap
void printHeap(int arr[], int n)
{
	cout << "Array representation of Heap is:\n";

	for (int i = 0; i < n; ++i)
		cout << arr[i] << " ";
	cout << "\n";
}

int main()
{
	cout << "Enter the size of the array:" ;
    int n;
    cin >> n;
    cout << "Enter the elements of the array: ";
    int arr[n];
    for(int i=0;i<n;i++)
    {
        cin >> arr[i];
    }

	buildHeap(arr, n);

	printHeap(arr, n);

	return 0;
}