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Quick Sort Algorithm

Quick Sort Algorithm

Do you know what is Quick Sort Algorithm? Have you ever thought about the process of the Quick Sort Algorithm? Let’s experience how we can implement the Quick Sort Algorithm.

But before we jump-start our programming concept of the Quick Sort Algorithm, let’s first come to know what sorting means in our daily life.

To the dictionary meaning, there are many ways any individual can explain the word ‘Sort’. This means anybody can use the ‘Sort’ word to remove any problem from their life. But we mainly deal with another meaning. Here, Sort means to rearrange something in an order.

In Programming there will be a lot of numbers & we need to develop an algorithm that sorts them in ascending order. That will be a very interesting topic.

But wait, is there any method present to solve such problems? Yes, there are!

 

What Is Sorting Algorithm? Get to Know More

Generally, an Algorithm means a set of lines of code. These types of lines help to solve out most common problems related to the programming field. The sorting Algorithm is such a kind of Algorithm. Here, a list of numbers will be provided to the developer. They need to sort them in ascending order.

If the numbers are very less like two or three numbers. Then it will be an easy task for the developer to sort them. They will use the swapping method among them & solve it.

But what if the numbers are 100s or 1000s? Then developers need to use Sorting Algorithms.

 

Types of Sorting Algorithm:

There is a plenty long list of Sorting Algorithms. Based on the situation, it is completely the developer’s choice to choose any Algorithms among the following.

Let’s make a list of the Sorting Algorithms:

  • Quick Sort
  • Selection sort
  • Bubble sort
  • Insertion sort
  • Merge sort
  • Heap sort
  • Counting sort
  • Radix sort
  • Bucket sort

 

What Is Quick Sort Algorithm? Read Below

Quick Sort AlgorithmBefore we provide the answer to the question “What is Quick Sort Algorithm”, Let’s know some brief history about this topic.

The Quick Sort Algorithm was developed by British computer scientist Tony Hoare in 1959. The name “Quick Sort” comes from the fact that it is capable of sorting a list of data elements significantly faster than other Sorting Algorithms.

It is a type of Sorting Algorithm & it completely works on Divide & Conquer Technique. Divide & Conquer Technique means that it first Divides the large set of data into small parts. Then again, those small parts are divided into smaller parts. At the very smallest part, this algorithm solves the problem & then Conquer all those parts & make again the full set of data.

We can list down the steps of the Quick Sort Algorithm:

  1. An array is divided into subarrays by selecting a pivot element (element selected from the array).
  2. While partitioning the array, the pivot element should be positioned in such a way that elements less than the pivot are kept on the left side, and elements greater than the pivot are on the right side of the pivot.
  3. The left and right subarrays are also divided using the same approach. This process continues until each subarray contains a single element. At this point, elements are already sorted. Finally, elements are combined to form a sorted array.

 

Implementation Of Quick Sort Algorithm:

  • Selection of Pivot Point: Depending on the programmer, the pivot element is selected at different positions. Some selected the first element of the array as the pivot, some selected any random number & some select the last one as the pivot. We here use the last element as the pivot element.
  • Partitioning The Array: Here, as per the pivot value, we need to partition the array. We need to swap the elements in the array in such a way that, the elements which are lesser than the pivot element will stay on the left side of the array. And the elements which are the higher value will stay on the right side of the pivot element. Let’s make a list of those steps.

 

  • A pointer is fixed at the pivot element. The pivot element is compared with the elements starting from the first index.
  • If the element is greater than the pivot element, a second pointer is set for that element.
  • Pivot is compared with other elements. If an element smaller than the pivot element is reached, the smaller element is swapped with the greater element found earlier.
  • Again, the process is repeated to set the next greater element as the second pointer. And, swap it with another smaller element.
  • The process continues until the second last element is reached. At last, the pivot element is swapped with the second pointer.

 

 

Partitioning the Array

 

  • Division of The Array: In this case, we need to divide the array. After placing the pivot element in its sorted position two arrays will be formed. Then again from those two subarrays, more subarrays will be divided. Till there is only one element present in those arrays. Hence, they will be already sorted. Then we add those subarrays & build the large array again.

Division of the Array

 

Programming Implementation of Quick Sort Algorithm:

  • Quick Sort Function:

Here, we need to take the array & its starting and ending index as arguments. If it is a normal array, then it will call the partitioning function. Also, after that, it will recursively call to itself.

By those two recursive callings, it is dividing the array into two subarrays. Before & after the pivot element the subarrays will create.

// Function Which Implements Quicksort

void quicksort(int a[], int begin, int end)    {

    // If Start Index Is Less Than The End One

    if (begin < end) 

    { 

        int p;

        // It Is The Partitioning Index

        p = partition(a, begin, end);

        // Recursively Calling Quicksort Function & Dividing Into Subarrays

        quicksort(a, begin, p - 1); 

        quicksort(a, p + 1, end); 

    }  }
  • Partitioning Function:

Here, in this function, we would take the pivot point as the last element of the array. Then we will run a loop there. If the elements in the array are lower than the pivot element then it will swap its position. This will go on till it reaches the endpoint of the array.

After that loop, the pivot element will be replaced with its sorted location. This will be implemented using the swapping method.

Also, at last, it will return the pivot element index to the called function.

// Function Which Implement Partitioning

int partition (int a[], int begin, int end) 

{ 

    // Declaring Pivot Element As The Endmost Of The Array

    int pivot = a[end];

    // Declaring Starting Index

    int i = (begin - 1);

    int j,t;

    // Loop For Checking Values With Pivot Value

    for (j = begin; j <= end - 1; j++) 

    { 

        // If Present Element Is Lower Than The Pivot 

        if (a[j] < pivot) 

        { 

            // Increasing Starting Index Value

            i++;

            // Swapping Two Consecutive Values

            t = a[i]; 

            a[i] = a[j];  

            a[j] = t; 

        } } 

    // Placing Pivot Element To Its Sorted Position

    t = a[i+1]; 

    a[i+1] = a[end]; 

    a[end] = t; 

    // Returning The Pivot Value To Quicksort Function

    return (i + 1); 

}
  • Main Function:

Here, we just need to take the user input values. Users need to provide the values to the array & as well. Then we will call only the Quick Sort function. Then it will do its task by itself.

int main()  { 

    int a[300],n,i;

    // Taking Input Of Array Size

    printf("Enter Size Of The Array: ");

    scanf("%d",&n);

    // Taking Inputs For Elements In Array

    for(i=0;i<n;i++)

        scanf("%d",&a[i]);

    // Printing The Original Array

    printf("Original Array :- \n"); 

    printArray(a, n);

    // Calling Quick Sort Function

    quicksort(a, 0, n - 1); 

    // Printing The Sorted Array

    printf("\nSorted Array :- \n");   

    printArray(a, n); 

    return 0;  }

Above are the code snippets. If needed, you can go through the full source code provided here. The probable output of the Quick Sort Algorithm will be the following.

Output:

Main function quick sort algorithm

Conclusion:

As we saw Quick Sort Algorithm is very important.

We should clear the basics of recursion & function calling for learning the Sorting Algorithm.

We should clear the partition method. That is very important among all the functions in the Quick Sort Algorithm.

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.

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Sanjana Grover
Sanjana Grover

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