heapsort.cpp

// Heap Sort Algorithm in C++

#include <iostream>

using namespace std;

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

void HeapSort(int arr[], int N)
{
    for (int i = N / 2 - 1; i >= 0; i--)
        heapify(arr, N, i);
 
    // One by one extract an element
    // from heap
    for (int i = N - 1; i > 0; i--) {
        // Move current root to end
        swap(arr[0], arr[i]);
        // call max heapify on the reduced heap
        heapify(arr, i, 0);
    }
}

int main()
{
    int arr[6] = {76, 22, 21, 96, 70, 20};
    HeapSort(arr, 6);
    
    return 0;
}

// Output

// 20 21 22 70 76 96