﻿ C# Sharp exercises: Heap Sort - w3resource

# C# Sharp Searching and Sorting Algorithm Exercises: Heap sort

## C# Sharp Searching and Sorting Algorithm: Exercise-5 with Solution

Write a C# Sharp program to sort a list of elements using Heap sort.

In computer science, heapsort (invented by J. W. J. Williams in 1964) is a comparison-based sorting algorithm. Heapsort can be thought of as an improved selection sort: like that algorithm, it divides its input into a sorted and an unsorted region, and it interactively shrinks the unsorted region by extracting the largest element and moving that to the sorted region. The improvement consists of the use of a heap data structure rather than a linear-time search to find the maximum. Although somewhat slower in practice on most machines than a well-implemented quicksort, it has the advantage of a more favorable worst-case O(n log n) runtime. Heapsort is an in-place algorithm, but it is not a stable sort.

A run of the heapsort algorithm sorting an array of randomly permuted values. In the first stage of the algorithm the array elements are reordered to satisfy the heap property. Before the actual sorting takes place, the heap tree structure is shown briefly for illustration.

Animation credits : RolandH

Sample Solution:-

C# Sharp Code:

``````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()+' ');
}

}
}

}
```
```

Sample Output:

```Original Array Elements :
2  5  -4  11  0  18  22  67  51  6

Sorted Array Elements :
-4  0  2  5  6  11  18  22  51  67
```

Flowchart:

C# Sharp Practice online:

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