heapify code code example

Example 1: Heap sort in c++

#include <iostream>
 
using namespace std;
 

void heapify(int arr[], int n, int i)
{
    int largest = i; 
    int l = 2 * i + 1;
    int r = 2 * i + 2;
 
    
    if (l < n && arr[l] > arr[largest])
        largest = l;
 
    
    if (r < n && arr[r] > arr[largest])
        largest = r;
 
    
    if (largest != i) {
        swap(arr[i], arr[largest]);
 
    
        heapify(arr, n, largest);
    }
}
 

void heapSort(int arr[], int n)
{

    for (int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i);
 

    for (int i = n - 1; i > 0; i--) {
       
        swap(arr[0], arr[i]);
        heapify(arr, i, 0);
    }
}
 

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

int main()
{
    int arr[] = { 12, 11, 13, 5, 6, 7 };
    int n = sizeof(arr) / sizeof(arr[0]);
 
    heapSort(arr, n);
 
    cout << "Sorted array is \n";
    printArray(arr, n);
}

Example 2: heap sort

// Heap Sort in C
  
  #include <stdio.h>
  
  // Function to swap the the position of two elements
  void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
  }
  
  void heapify(int arr[], int n, int i) {
    // Find largest among root, left child and right child
    int largest = i;
    int left = 2 * i + 1;
    int right = 2 * i + 2;
  
    if (left < n && arr[left] > arr[largest])
      largest = left;
  
    if (right < n && arr[right] > arr[largest])
      largest = right;
  
    // Swap and continue heapifying if root is not largest
    if (largest != i) {
      swap(&arr[i], &arr[largest]);
      heapify(arr, n, largest);
    }
  }
  
  // Main function to do heap sort
  void heapSort(int arr[], int n) {
    // Build max heap
    for (int i = n / 2 - 1; i >= 0; i--)
      heapify(arr, n, i);
  
    // Heap sort
    for (int i = n - 1; i >= 0; i--) {
      swap(&arr[0], &arr[i]);
  
      // Heapify root element to get highest element at root again
      heapify(arr, i, 0);
    }
  }
  
  // Print an array
  void printArray(int arr[], int n) {
    for (int i = 0; i < n; ++i)
      printf("%d ", arr[i]);
    printf("\n");
  }
  
  // Driver code
  int main() {
    int arr[] = {1, 12, 9, 5, 6, 10};
    int n = sizeof(arr) / sizeof(arr[0]);
  
    heapSort(arr, n);
  
    printf("Sorted array is \n");
    printArray(arr, n);
  }

Example 3: heapify down

Heapify down is used when we remove the top element from a heap. Removal of an element is done by swapping the top element with the last element at the bottom of the tree, removing the last element, and then heapfying the new top element down to maintain the heap property. Because this moves down the heap tree, it must perform two comparisons per iteration, with the left child and the right child elements, then swap with the smaller one. Because of this, heapify down is usually more complex to implement than heapify up.