Implementing quicksort algorithm

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I found quicksort algorithm from this book

This is the algorithm

QUICKSORT (A, p, r)
if p < r
    q = PARTITION(A, p, r)
    QUICKSORT(A, p, q-1)
    QUICKSORT(A, q+1, r)

PARTITION(A, p, r)
x=A[r]
i=p-1
for j = p to r - 1
  if A <= x
     i = i + 1
     exchange A[i] with A[j]
exchange A[i+1] with A[r]
return i + 1

And I made this c# code:

private void quicksort(int[] input, int low, int high)
{
    int pivot_loc = 0;

    if (low < high)
        pivot_loc = partition(input, low, high);
    quicksort(input, low, pivot_loc - 1);
    quicksort(input, pivot_loc + 1, high);
}

private int partition(int[] input, int low, int high)
{
    int pivot = input[high];
    int i = low - 1;

    for (int j = low; j < high-1; j++)
    {
        if (input[j] <= pivot)
        {
            i++;
            swap(input, i, j);
        }
    }
    swap(input, i + 1, high);
    return i + 1;
}



private void swap(int[] ar, int a, int b)
{
    temp = ar[a];
    ar[a] = ar[b];
    ar[b] = temp;
}

private void print(int[] output, TextBox tbOutput)
{
    tbOutput.Clear();
    for (int a = 0; a < output.Length; a++)
    {
        tbOutput.Text += output[a] + " ";
    }
}

When I call function like this quicksort(arr,0,arr.Length-1); I get this error An unhandled exception of type 'System.StackOverflowException' occurred it pass empty array... when call function like this quicksort(arr,0,arr.Length); I get error Index was outside the bounds of the array. on this line int pivot = input[high]; but array passed successfully.

I also want to print it like this print(input,tbQuick); but where to place it so it would print when quicksort finished?

You did not properly implement the base case termination, which causes quicksort to never stop recursing into itself with sublists of length 0.

Change this:

if (low < high)
    pivot_loc = partition(input, low, high);
quicksort(input, low, pivot_loc - 1);
quicksort(input, pivot_loc + 1, high);

to this:

if (low < high) {
    pivot_loc = partition(input, low, high);
    quicksort(input, low, pivot_loc - 1);
    quicksort(input, pivot_loc + 1, high);
}

QuickSort, Compare the pivot to the value to its right. The Quicksort algorithm picks an element as pivot and partition the given array around the selected pivot element. There are many ways the pivot element can be selected. Those are:-Always pick the first element as a pivot. Always pick the last element as pivot. Pick random element as pivot. Pick the middle element or median as a pivot.

In addition to Deestan's answer, you also have this wrong:

for (int j = low; j < high-1; j++)

It should be:

for (int j = low; j < high; j++)

Quicksort Algorithm, Quicksort is a sorting algorithm, which is leveraging the divide-and-conquer principle. It has an average O(n log n) complexity and it's one of the  Quicksort sorting technique is widely used in software applications. Quicksort uses a divide-and-conquer strategy like merge sort. In the quicksort algorithm, a special element called “pivot” is first selected and the array or list in question is partitioned into two subsets. The partitioned subsets may or may not be equal in size.

Just in case you want some shorter code for Quicksort:

    IEnumerable<int> QuickSort(IEnumerable<int> i)
    {
        if (!i.Any())
            return i;
        var p = (i.First() + i.Last) / 2 //whichever pivot method you choose
        return QuickSort(i.Where(x => x < p)).Concat(i.Where(x => x == p).Concat(QuickSort(i.Where(x => x > p))));
    }

Get p (pivot) with whatever method is suitable of course.

Quicksort Algorithm Implementation in Java, How do we implement it?. Since the Array prototype method sort uses its own sorting algorithm, we cannot use it for implementing quicksort. We must create a  Quicksort is one of the most widespread sorting algorithm due to the relative simplicity of implementation and efficient performance. In this article, we'll implement Quicksort in Python. Introduction Quicksort is a popular sorting algorithm and is often used, right alongside Merge Sort.

This is the shortest implementation of Quick Sort algorithm

IEnumerable<T> QuickSort<T>(IEnumerable<T> i) where T :IComparable
{
    if (!i.Any()) return i;
    var p = i.ElementAt(new Random().Next(0, i.Count() - 1));
    return QuickSort(i.Where(x => x.CompareTo(p) < 0)).Concat(i.Where(x => x.CompareTo(p) == 0)).Concat(QuickSort(i.Where(x => x.CompareTo(p) > 0)));
}

Implementing Quicksort in JavaScript - Charles Stover, Quicksort is an efficient sorting algorithm. Developed by British Although quicksort can be implemented as a stable sort using linked lists, it will often suffer from poor pivot choices without random  Quicksort or partition-exchange sort, is a fast sorting algorithm, which is using divide and conquer algorithm. Quicksort first divides a large list into two smaller sub-lists: the low elements and the high elements. Quicksort can then recursively sort the sub-lists. Steps to implement Quick sort: 1) Choose an element, called pivot, from the

A Simple Quick Sort Implementation.

https://github.com/bharathkumarms/AlgorithmsMadeEasy/blob/master/AlgorithmsMadeEasy/QuickSort.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace AlgorithmsMadeEasy
{
    class QuickSort
    {
        public void QuickSortMethod()
        {
            var input = System.Console.ReadLine();
            string[] sInput = input.Split(' ');
            int[] iInput = Array.ConvertAll(sInput, int.Parse);

            QuickSortNow(iInput, 0, iInput.Length - 1);

            for (int i = 0; i < iInput.Length; i++)
            {
                Console.Write(iInput[i] + " ");
            }

            Console.ReadLine();
        }

        public static void QuickSortNow(int[] iInput, int start, int end)
        {
            if (start < end)
            {
                int pivot = Partition(iInput, start, end);
                QuickSortNow(iInput, start, pivot - 1);
                QuickSortNow(iInput, pivot + 1, end);
            }
        }

        public static int Partition(int[] iInput, int start, int end)
        {
            int pivot = iInput[end];
            int pIndex = start;

            for (int i = start; i < end; i++)
            {
                if (iInput[i] <= pivot)
                {
                    int temp = iInput[i];
                    iInput[i] = iInput[pIndex];
                    iInput[pIndex] = temp;
                    pIndex++;
                }
            }

            int anotherTemp = iInput[pIndex];
            iInput[pIndex] = iInput[end];
            iInput[end] = anotherTemp;
            return pIndex;
        }
    }
}

/*
Sample Input:
6 5 3 2 8

Calling Code:
QuickSort qs = new QuickSort();
qs.QuickSortMethod();
*/

Quicksort, The values of k1 and k2 depend on the implementation of the algorithms, the computer used etc. In practice, if you ran quick sort and merge sort on the same  Implementing quicksort algorithm. This is the shortest implementation of Quick Sort algorithm. A Simple Quick Sort Implementation.

Quicksort algorithm overview | Quick sort (article), Data Structure and Algorithms - Quick Sort - Quick sort is a highly efficient sorting To know about quick sort implementation in C programming language,  QuickSort can be implemented in different ways by changing the choice of pivot, so that the worst case rarely occurs for a given type of data. However, merge sort is generally considered better when data is huge and stored in external storage. Is QuickSort stable? The default implementation is not stable.

Data Structure and Algorithms - Quick Sort, Quicksort or partition-exchange sort, is a fast sorting algorithm, which is using divide and conquer algorithm. Quicksort first divides a large list into two smaller sub-  Last Updated on August 13, 2019 Why would you ever implement machine Read more

Implement quick sort in java., This article describes how to implement Quicksort with Java. 1. Quicksort. 1.1. Overview. Sort algorithms order the elements of an  Quick sort is a highly efficient sorting algorithm and is based on partitioning of array of data into smaller arrays. A large array is partitioned into two arrays one of which holds values smaller than the specified value, say pivot, based on which the partition is made and another array holds values greater than the pivot value.

Comments
  • I do not understand the last part of the question - the print thing - as your code doesn't show the bit where you're actually calling quicksort. Why not just print as the next statement after calling quicksort?
  • Because my code had infinitive loop so I didn't know here to put the print to print once... Now is ok..
  • Just wrap the recursive function in another function to print it when it is done sorting.
  • actually i get first time code from here algorithmist.com/index.php/Quicksort and then checked book and it was almost same... didnt see
  • but you right... It was giving me wrong result after change it to high it worked... I didn't know books have errors o_0
  • This is 2way or 3way quicksort?
  • standard 2 way -- you sub-divide the partition into 2 more partitions on each recursive sort.
  • Ok thanks I wanted to confirm it.. I couldn't find anywhere good 3-way quicksort algorithm... Do you know how to do it or you know where i can find?
  • You are misusing Random. Either pass in a Random parameter into the QuickSort function or refer to a single instance outside of the method's scope. Initialization reseeds the object, which can result in not-so-random results if executed very quickly.
  • As mentioned 'p' can be obtained with whatever method is most appropriate - it's the method size I'm demonstrating for here, but yes your points regarding random are correct.