heap sort algorithm tutorial code example

Example 1: heap sort

// @see https://www.youtube.com/watch?v=H5kAcmGOn4Q

function heapify(list, size, index) {
    let largest = index;
    let left = index * 2 + 1;
    let right = left + 1;
    if (left < size && list[left] > list[largest]) {
        largest = left;
    }
    if (right < size && list[right] > list[largest]) {
        largest = right;
    }
    if (largest !== index) {
        [list[index], list[largest]] = [list[largest], list[index]];
        heapify(list, size, largest);
    }
    return list;
}

function heapsort(list) {
    const size = list.length;
    let index = ~~(size / 2 - 1);
    let last = size - 1;
    while (index >= 0) {
        heapify(list, size, --index);
    }
    while (last >= 0) {
        [list[0], list[last]] = [list[last], list[0]];
        heapify(list, --last, 0);
    }
    return list;
}

heapsort([4, 7, 2, 6, 4, 1, 8, 3]);

Example 2: heapsort

Implementation of heap sort in C++:

#include <bits/stdc++.h>
using namespace std;

// To heapify a subtree rooted with node i which is
// Heapify:- A process which helps regaining heap properties in tree after removal 
void heapify(int A[], int n, int i)
{
   int largest = i; // Initialize largest as root
   int left_child = 2 * i + 1; // left = 2*i + 1
   int right_child = 2 * i + 2; // right = 2*i + 2

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

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

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

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

// main function to do heap sort
void heap_sort(int A[], int n)
{
   // Build heap (rearrange array)
   for (int i = n / 2 - 1; i >= 0; i--)
       heapify(A, n, i);

   // One by one extract an element from heap
   for (int i = n - 1; i >= 0; i--) {
       // Move current root to end
       swap(A[0], A[i]);

       // call max heapify on the reduced heap
       heapify(A, i, 0);
   }
}

/* A  function to print sorted Array */
void printArray(int A[], int n)
{
   for (int i = 0; i < n; ++i)
       cout << A[i] << " ";
   cout << "\n";
}

// Driver program
int main()
{
   int A[] = { 22, 19, 3, 25, 26, 7 }; // array to be sorted
   int n = sizeof(A) / sizeof(A[0]); // n is size of array

   heap_sort(A, n);

   cout << "Sorted array is \n";
   printArray(A, n);
}

Example 3: heap sort

# Heap Sort in python


  def heapify(arr, n, i):
      # Find largest among root and children
      largest = i
      l = 2 * i + 1
      r = 2 * i + 2
  
      if l < n and arr[i] < arr[l]:
          largest = l
  
      if r < n and arr[largest] < arr[r]:
          largest = r
  
      # If root is not largest, swap with largest and continue heapifying
      if largest != i:
          arr[i], arr[largest] = arr[largest], arr[i]
          heapify(arr, n, largest)
  
  
  def heapSort(arr):
      n = len(arr)
  
      # Build max heap
      for i in range(n//2, -1, -1):
          heapify(arr, n, i)
  
      for i in range(n-1, 0, -1):
          # Swap
          arr[i], arr[0] = arr[0], arr[i]
  
          # Heapify root element
          heapify(arr, i, 0)
  
  
  arr = [1, 12, 9, 5, 6, 10]
  heapSort(arr)
  n = len(arr)
  print("Sorted array is")
  for i in range(n):
      print("%d " % arr[i], end='')