programming-examples/c-sharp/Sorting/C# Sharp program to sort a list of elements using Heap sort.cs

using System;

namespace Heap_sort
{
public class MainClass
{
    public static void Main (string[] args)
    {
        int[] mykeys = new int[] {2, 5, -4, 11, 0, 18, 22, 67, 51, 6};
        //double[] mykeys = new double[] {2.22, 0.5, 2.7, -1.0, 11.2};
        //string[] mykeys = new string[] {"Red", "White", "Black", "Green", "Orange"};
        Console.WriteLine("\nOriginal Array Elements :");
        printArray (mykeys);
        heapSort (mykeys);
        Console.WriteLine("\n\nSorted Array Elements :");
        printArray (mykeys);
        Console.WriteLine("\n");
    }

private static void heapSort<T> (T[] array) where T :
    IComparable<T>
    {
        int heapSize = array.Length;

        buildMaxHeap (array);

        for (int i = heapSize-1; i >= 1; i--)
            {
                swap (array, i, 0);
                heapSize--;
                sink (array, heapSize, 0);
            }
    }

private static void buildMaxHeap<T> (T[] array) where T :
    IComparable<T>
    {
        int heapSize = array.Length;

        for (int i = (heapSize/2) - 1; i >= 0; i--)
            {
                sink (array, heapSize, i);
            }
    }

private static void sink<T> (T[] array, int heapSize, int toSinkPos) where T :
    IComparable<T>
    {
        if (getLeftKidPos (toSinkPos) >= heapSize)
            {
                // No left kid => no kid at all
                return;
            }


        int largestKidPos;
        bool leftIsLargest;

        if (getRightKidPos (toSinkPos) >= heapSize || array [getRightKidPos (toSinkPos)].CompareTo (array [getLeftKidPos (toSinkPos)]) < 0)
            {
                largestKidPos = getLeftKidPos (toSinkPos);
                leftIsLargest = true;
            }
        else
            {
                largestKidPos = getRightKidPos (toSinkPos);
                leftIsLargest = false;
            }



        if (array [largestKidPos].CompareTo (array [toSinkPos]) > 0)
            {
                swap (array, toSinkPos, largestKidPos);
                if (leftIsLargest)
                    {
                        sink (array, heapSize, getLeftKidPos (toSinkPos));
                    }
                else
                    {
                        sink (array, heapSize, getRightKidPos (toSinkPos));
                    }
            }

    }

    private static void swap<T> (T[] array, int pos0, int pos1)
    {
        T tmpVal = array [pos0];
        array [pos0] = array [pos1];
        array [pos1] = tmpVal;
    }

    private static int getLeftKidPos (int parentPos)
    {
        return (2 * (parentPos + 1)) - 1;
    }

    private static int getRightKidPos (int parentPos)
    {
        return 2 * (parentPos + 1);
    }

    private static void printArray<T> (T[] array)
    {
        foreach (T t in array)
            {
                Console.Write(' '+t.ToString()+' ');
            }
    }
}

}