If you are a newcomer to the Computer Science course, you will probably come across different types of Algorithms & Data Structure Concepts. Among them, the Sorting Algorithms are major ones where the “Quick Sort Algorithm” is worth noting.
Do you know about the Quick Sort Algorithm concept in Computer Science? If you don’t know that, this article will be enough to highlight the major part of the Quick Sort Algorithm & its implementation process in C programming language.
So, let us start our extensive discussion to the depth of the Sorting Algorithm Quick Algorithm without wasting much time.
Summary or Key Highlights:
- The Quicksort Algorithm is a prominent Data Structure & Algorithm Concept.
- The Quicksort Algorithm discusses the sorting method of any unsorted array.
- The Quicksort Algorithm is developed on picking up the right pivot element from the array.
- The Algorithm Quick Sort uses the Divide and Conquer policy to get the required answer.
- The Quicksort Algorithm can only be developed in optimized manner using Recursion.
- The Time Complexity of Algorithm Quick Sort can be divided into three categories.
What Is Quick Sort Algorithm In Data Structure?
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 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 Covers all those parts & makes again the full set of data.
We can list down the steps of the Quick Sort Algorithm:
- An array is divided into subarrays by selecting a pivot element (element selected from the array).
- 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.
- 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.
How Quick Sort Algorithm Works?
- 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 selected the last one as the pivot.
- 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. Let’s make a list of those steps.
Let’s discuss these both steps properly with an image to clarify the concept in a better way.
- 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.
What Is The Algorithm of Quick Sort Method?
Now, as the concept of the Quick Sort becomes clear with the above steps & images, we can now freely move for the implementation process. However, before implementing the complete code within the C programming language, the preview of it should be discussed.
And we are talking about the Algorithm of Quick Sort Method. In the Quick Sort Implementation process, there are many functions present. However, we will look into the algorithm of the function named Quick Sort which is the main driving force of the process. Also, if you’re interested in knowing about the implementation process of Quick Sort for programming languages like Python, then you can check out our article on Quick Sort in Python.
Here is the algorithm of the Quick Sort Method. On which we will implement the Quick Sort Function.
QUICK (array, start, end) {
if (start < end) {
p = part (array, start, end)
QUICK (array, start, p - 1)
QUICK (array, p + 1, end)
}}
What Will Be The Pseudo Code of Quick Sort Algorithm?
Now, as we are approaching towards central idea of the article, the implementation of Quick Sort with the help of C programming language, we have to dive into the programming world. Above mentioned Algorithm is now going to be changed more to a programming one.
We will implement the Pseudo Code of the Quick Sort Algorithm that will clarify & build a foundation in your mind about the implementation process. At this time, we are not going to only build the Pseudo Code of the Quick Sort Function.
Rather, we will implement the Pseudo Code of the Partition Function as well. So, let us have a look at the following Pseudo Code.
Pseudo Code of Quick Sort Function:
function quicck(arr, l, r)
if l < r
pivot = part(arr, l, r)
quick(arr, l, pivot - 1)
quick(arr, pivot + 1, r)
Pseudo Code of Partition Function:
function part(arr, l, r)
pivot = arr[r]
i = l - 1
for j = l to r - 1
if arr[j] < pivot
i = i + 1
swap arr[i] and arr[j]
swap arr[i + 1] and arr[r]
return i + 1
Implementation Method of Quick Sort Algorithm
Now, it is time to discuss the Quick Sort Implementation process in the C programming language. To develop a complete working program, there are three major functions we have to include. One is the Quick Sort Function & another is the Partition function.
Along with these two, there is also the Main Function present from where all functions will start execution. We will start with the Quick Sort Function Code Snippet along with is detailed discussion in a step-by-step format.
Quick Sort Function:
// 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);
} }
Steps of the Program:
- 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.
- 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 be created.
Partitioning 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);
}
Steps of The Program:
- Here, in this function, we would take the pivot point as the last element of the array.
- 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.
Main Function:
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; }
Steps of the Program:
- Declare a long array to take the inputs from the user.
- Take the size & elements of the string from the user. Enter them into the variables.
- Now, with the print function, we will print the normal array.
- The Quick Sort function will be called there.
- After operation, the array will again be printed to see the changes.
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:
Time and Space Complexities of the Quick Sort Algorithm:
It is time to discuss the Time & Space Complexities of the Quick Sort Method. To judge each sorting method & algorithm, there are certain parameters present. These parameters are the Time Complexity & Space Complexity.
The Time Complexity is the time measurement policy that let us to know what time it will take for the best case & for the worst case. The time complexity of Quick Sort Method is the following.
- For the Best Case, Time Complexity O(n*logn)
- For the Average Case, Time Complexity O(n*logn)
- For the Worst Case, Time Complexity O(n2)
Now, it is time to discuss the Space Complexity. There is no Best & Worst Case present for the Space Complexity. The Space Complexity will be the same for the each case. The Space Complexity of the Quick Sort Method is O(n*logn)
Why We Use Quick Sort Algorithm?
There are many reasons behind the need for the Quick Sort Method to be used. From the above discussion, it might become clear that the Quick Sort Process helps to filter the data sequence. Also, using this method, one unsorted data can be sorted.
This is the major reason behind the use of the Quick Sort Method. The Quick Sort Method is one of the fastest sorting algorithms that will filter the dataset in a certain manner. This helps to figure out any large data set based on Date, Time, Age of any individual, etc.
From Commercial Commutating to Information Searching, the Quick Sort is used everywhere. Also, we need to use the Quick Sort Method to check whether any algorithm is stable or not. If the Algorithm is not stable, the use of Quick Sort is inevitable.
Just like Quick Sort, Bubble Sort is also an important concept. It also has many uses and advantages across all the programming languages. We’ve written a detailed article on Bubble Sort in Java to clear the concept more efficiently.
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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Takeaways:
- The Quick Sort Process depends upon the Pivot Element choosing process.
- Based upon the Pivot element, the entire list of unsorted array is divided.
- The Elements those are less than Pivot Number Placed at left side.
- For the higher numbers, the elements will be placed on the right sides.
- The swapping method can only be used for changing the values within the array.
- The Quick Sort function in the code will be the major stake that will be called multiple times.
- The Best Time Complexity of the Quick Sort will be the O(n*logn).
FAQs (Frequently Asked Question by Students)
The Quick Sort is the algorithm that is used to sort an unsorted data sequence in the ascending order. There is a need to pick up a pivot element. And based on the pivot element, the number gets sorted in the same array without any error.
The fastest sorting algorithm is the Quick Sort. It takes only O(n*long) time to complete any best case. Also, the same is the average time of the algorithm. So, the Quick Sort is the fastest among other sorting algorithms like Selection, Bubble, etc.
The Quick Sort method is the example of Divide and Conquer. The large data array is divided into small parts. And then the solutions of those small parts are calculated. Later, those solutions are added to get the large & required solution. It is known as the Divide & Conquer method.
