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How to sort array with heap sort?

C#  |  .NET  |  Algorithms

The heap sort first builds a max-heap from the array (the heapify operation). Then, it repeats a few steps until there is only one element in the heap. The mentioned steps are as follows:

  • 1. Swap the first element (root with the maximum value) with the last element.
  • 2. Remove the last element (which is currently the maximum value) from the heap.
  • 3. Build the max-heap again.

The code is as follows:

void Sort(int[] a)
    for (int i = a.Length / 2 - 1; i >= 0; i--)
        Heapify(a, a.Length, i);

    for (int i = a.Length - 1; i > 0; i--)
        (a[0], a[i]) = (a[i], a[0]);
        Heapify(a, i, 0);

The code of the auxiliary Heapify method is shown below:

void Heapify(int[] a, int n, int i)
    int max = i;
    int l = 2 * i + 1;
    int r = 2 * i + 2;

    max = l < n && a[l] > a[max] ? l : max;
    max = r < n && a[r] > a[max] ? r : max;

    if (max != i)
        Swap(a, i, max);
        Heapify(a, n, max);

This entry can contain content, including parts of code, from one of my books, namely from the Second Edition of C# Data Structures and Algorithms, published by Packt Publishing in 2024. If you want to read more about the heap sort algorithm, as well as about other kinds of sorting algorithms, I encourage you to take a look at the mentioned book. You can buy it here.

The content, including any part of code, is presented without warranty, either express or implied. The author cannot be held liable for any damages caused or alleged to have been caused directly or indirectly by any content shown on this website.

Hello, I am Marcin

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If you want to learn data structures and algorithms in the context of C#, let's take a look at my newest book. It is the second edition of C# Data Structures and Algorithms. You can buy it here.


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