# What Is Quicksort In Python? Algorithms Explained

Do you know what is Quicksort in Python programming language? Have you ever thought about how does Quicksort work in Python programming language? Let us try to understand this concept  in this article. Also, if you’re curious to know what are the ways implement it and need help with Python homework then this article is for you.

But before we move ahead with our discussion on Quicksort in Python programming language, we should be aware of the basic of the Quicksort algorithm. We must find out its root before moving ahead in our discussion.

So, let us start our journey from the basic of the sorting algorithm present in computer science. Then we will move towards the discussion on Quicksort algorithm in Python programming language.

## What Is Sorting Algorithm & Its Different Types? Get To Know

In computer science, there is a special section present on the Data Structure topic. And the section is known as the Sorting Algorithm section. Though, this section belongs in the intermediate position between the Data Structure & Algorithm.

From the word “Sorting”, a very basic understanding should come to your mind that we are going to discuss something to Sort. In the sorting algorithms, we should sort a list of elements present as any Data Structure in the program.

The elements are numbers or integers. But sometimes, it can be a character element also. But now, you might think, why is it so important? Is there any reason to pay more importance to this section?

Now, the answer to your query will be Yes! You should pay good attention to Sorting Algorithms in computer science. Because they are the magic keys to solving any difficult problems in the future.

So, you should not neglect it by assuming it is a simple algorithm. There is another reason that makes sorting algorithms more important.

That is the presence of a large list of sorting algorithms. There are likely nine different sorting algorithms present. Now, as a developer, you should choose a particular algorithm to solve any problem.

As different sorting algorithm takes different time for solving different problems. So, picking up the most appropriate sorting algorithm will be a difficult task for the developer. So, you should solve more & more problems to come out of the situation.

###### The lists of different sorting algorithms are below:
1. Quick Sort
2. Selection sort
3. Bubble sort
4. Insertion sort
5. Merge sort
6. Heap sort
7. Counting sort
9. Bucket sort

But it is not our target to discuss every algorithm in this article. We are going to focus on the Quicksort algorithm in Python programming language.

So, we are now quite sure that the background of the Quicksort algorithm is clear to you. So now, we will discuss the basic of Quicksort in Python programming language before moving to its implementation process.

## What Is Quicksort In Python Programming Language? Read Below

The Quicksort algorithm is a special sorting algorithm present in computer science. The Quicksort algorithm was first discovered in 1959. The name “Quick Sort” comes from its speed to sort any number of elements provided as an array in the problem.

And it is a fact that, in some cases, the Quicksort algorithm can work more smoothly & faster manner than any other sorting algorithm. But if you think that, you are going to use this sorting algorithm for every problem, then you will commit a mistake.

Because, in some cases, the Quicksort algorithm doesn’t perform well. In the worst-case scenario of any problem, the Quicksort algorithm can provide time complexity up to O(N2). So, you should choose this algorithm for some long arrays in the problem.

Now one question might arise in your mind is Quicksort in place algorithm? Because such parameters are necessary to judge any sorting algorithms. And the Quicksort algorithm is a completely In-Place algorithm.

The Quicksort algorithm depends upon the strategy of Divide & Conquer. That means a large set of data will be first divided into some small pieces. Now, those small pieces will be evaluated & at the end, they will be again combined to get the full result.

Following the same manner, the Quicksort algorithm first divides a set of elements into two pieces. Now, those two pieces will again divide into two small pieces. In this way, when the pieces become very small they are calculated.

In the end, all those results are merged & the final result is produced. And the element by which basis the division of the element set happens are known as the Pivot element in the Quicksort algorithm.

The Quicksort algorithm is highly used in the C programming language. As you know the concept of Data Structure & Algorithm is highly dependent upon the C programming language. But with time, the concept has been changed.

Python & Java programming languages are used for the implementation of different applications in the Information Technology industry. So, while the development of such application use of sorting algorithms are necessary.

That is the reason; now all of such sorting algorithms are present in Java & Python programming languages. But the development process of such an algorithm is still the same. The development process is not changed with the programming language.

Now, after a brief discussion about the Quicksort algorithm, we should move ahead with the development process in the Python programming language. But direct implementation of the Quicksort algorithm in Python programming language will bring some issues.

So, let us first discuss the algorithm of the Quicksort in Python programming language. Then we will move to the implementation process.

If you wish to know more about Quicksort Algorithm then you can check out our article on “Quicksort Algorithm“.

### What Are The Steps In Quicksort Algorithm?

The algorithm of the Quicksort technique will help to visualize the implementation process in Python programming language. The steps which are going to mention here will be implemented the same inside the program.

So, we should pay attention to the steps required for the Quicksort algorithm. And the required steps are following:

• At first, the pivot element should be declared inside of the program. Here, the pivot element can be any element from the set provided in the program. But mainly, the first or last element is chosen as the pivot element. Sometimes, the mid element can also be chosen.
• After getting the Pivot element, we should break down the list of elements into two parts. The one part will be on the left side of the Pivot element. And another will be on the right side of the Pivot element. Now, these two parts have been taken into consideration.
• Inside those two sub-parts, the pivot element will again be picked up. And based upon that pivot element, those sub-parts will again divide into the smaller sub-parts. In this way, the complete process will be executed.
• The same process will be followed recursively after & after till we are not receiving any sub-parts having only two or three elements. Now, those elements will be sorted & the result sub-part will be produced.
• At the last, all the mini sub-parts are going to merge. And hence, the total lists of the elements are now present in front of the programmer. And hence, there are no more tasks present to complete the Quicksort algorithm.

Now, after the completion of the algorithm process for Quicksort, we should move ahead with the implementation process. But before the final implementation in Python programming language, let us do a mini implementation.

### What Is The Pseudo-Code Of The Quicksort Algorithm In Python Programming Language?

Pseudo-codes are the higher form of the algorithms. Any algorithm can be defined using Pseudo-codes for getting a better blueprint of any process. We are going to do the same thing for the Quicksort algorithm process.

Pseudo-codes are not complete code nor is it following any programming languages for the implementation process. With any normal textual language, it can be defined. The goal is to find out the complete workflow of the program.

So, the Pseudo-code of the Quicksort algorithm is following:

```function-quicksort(arr)

check length(arr) <= 1

back arr

otherwise: change pivot = arr[0]

change left side = Null array

change right side = Null array

for each element ele in arr[1:]

check ele < pivot

otherwise: add ele to right side

call again function-quicksort(left side)

call again function-quicksort(right side)

back all data

```

Now, after discussing the Pseudo-code of the Quicksort algorithm, we are free to move for the implementation process of it using the Python programming language. But before moving ahead with that, we should focus on a very important question.

### Does Recursion Require In Quicksort Algorithm In Python Programming Language?

Without discussing this important question, it will not be fair to move ahead. As recursion is the pillar of the Quicksort algorithm process. Without the recursion method, we can’t implement the Quicksort algorithm in Python programming language.

But there is no need to think that, as we are using the Python programming language, we have to use the recursion method. This concept is completely wrong. Without the use of recursion, one can’t even develop the Quicksort algorithm in C programming language also.

Recursion is a method that calls the same function again & again time from the said function only. In this way, some processes are completed. It works similarly to the loop concept, but it takes small space.

Now, you might ask can Quicksort algorithm be implemented without using the recursion method.

Yes! The Quicksort algorithm can be implemented without using the recursion method. Other sorting algorithms can also be implemented without using the same. But in that case, they will take a long time to get the solution to the problem.

In those cases, we should develop one for loop to check & divide the set of elements in the program. This is the reason, instead of using the iteration method; the recursion method is used highly in the sorting algorithms.

Now, we hope that the need for the recursion method is clear in your mind. Now, we are all set for the implementation process of the Quicksort algorithm in Python programming language. So, let us implement that now.

### What Is The Way To Implement Quicksort Algorithm In Python Programming Language?

Now, we will implement the Quicksort algorithm using the Python programming language. In this case, we will provide the unsorted array inside of the program. But using the input concept in Python programming language, we can take it from the users also.

For the implementation process, there is no need to import any library function inside the program. We will directly start the implementation process. We will declare one function inside the program.

This function will first check the length of the array. If the length is zero or negative, then the program will be concluded. Else, the program will find out the pivot element from the array. The first element is considered as the pivot element.

Now, all the elements that have a value less than the pivot element will be placed inside of the left sub-array. And all the elements that have more values will be placed inside the right sub-array. We will declare some for loop for the checking purpose.

Now, the left & right subarrays will recursively call the same function & get the final result.

##### Example:

```def qsort(x): # Declaration Of The Function

if len(x) <= 1: # Checking The Length or End Condition

return x # Returning The Value

else: # For Other Condition

p = x[0] # Getting Pivot Value

l = [k for k in x[1:] if k < p] # Generating Left Sub Array

r = [k for k in x[1:] if k >= p] # Generating Right Sub Array

return qsort(l) + [p] + qsort(r) # Recursively Calling The Function

a = [4, 2, 7, 2, 1] # Assigning The Unsorted String Value

print("Unsorted Array: ", a) # Printing The Original Element

b = qsort(a) # Calling The Function```

Let us try to find out the output of the above code. It will help to understand the implementation process of the Quicksort algorithm in Python programming language.

## Conclusion:

As we saw, the Quicksort in Python programming language is very important to know.

Quicksort algorithm in Python programming language is dependent upon the successful implementation of the recursion method inside of the program.

It is advisable to clear a basic understanding of the Python programming language before moving into the development process. Also, the Data Structure concept should be cleared.

So, hope you have liked this piece of article. Share your thoughts in the comments section and let us know if we can improve more.