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In this problem statement, our aim is to sort an array recursively using merge sort and implement the code with the help of Javascript. So below we will discuss Merge sort and its implementation.

Understanding the problem statement

The problem statement is to write a function for merge sort in Javascript that will help to sort the given input array into an ascending or descending order. And we have to create a function which will sort the elements recursively.

What is the recursive sorting technique?

Recursion is a technique in which a function calls itself to solve a problem. When a function calls itself then it creates a new instance of itself on the stack and the function continues to execute until a required result is not found. This result is the condition that stops the recursion and allows the function to give the result.

What is a merge sort Algorithm?

In the merge sort, the algorithm sorts an array recursively by breaking it down into smaller subarrays until each subarray consists of one element in it. Then the algorithm combines the adjacent pairs of subarrays into larger and sorted subarrays. This process runs recursively until the whole element of the array is not sorted.

For the code we will create a function to do the merge sort. And inside the function we will divide an array into smaller subarrays, sorting those subarrays recursively and then merge them back together in order to produce a fully sorted array. The key operation of the function is the merge step where two sorted subarrays are combined into a single sorted array.

Algorithm

Step 1 − Declare a function called mergeSort which is using a parameter of array.

Step 2 − Inside the function, we will check if the length of the array is 1 or less than 1 its already sorted so just return the array.

Step 3 − Otherwise, we will divide the array into two half arrays left and right and recursively sort every half part using mergeSort.

Step 4 − And once the recursive calls return we will merge the sorted left and right parts together using the merge function.

Step 5 − The merge function will take two sorted arrays left and right and merge them into a single sorted array as the result.

Code for the algorithm function mergeSort(arr) { if (arr.length <= 1) { return arr; } const mid = Math.floor(arr.length / 2); const left = arr.slice(0, mid); const right = arr.slice(mid); return merge(mergeSort(left), mergeSort(right)); } function merge(left, right) { const result = []; while (left.length && right.length) { if (left[0] < right[0]) { result.push(left.shift()); } else { result.push(right.shift()); } } return [...result, ...left, ...right]; } const arr = [4, 1, 5, 2, 6, 3, 7, 8]; console.log(mergeSort(arr)); Complexity

The time taken by the mergeSort function is O(n log n) because we have implemented merge sort which takes O(n log n) time to sort the items. And n is the size of the given array. And the space used by the code is also O(n) as it is storing the result as a sorted array. So this technique makes it an efficient sorting algorithm for large datasets.

Conclusion

So the above created function can be used to sort the given array of size n with time complexity O(n log n). This is a reliable and efficient sorting algorithm.

You're reading Using Merge Sort To Recursive Sort An Array Javascript

## Quick Sort In Data Structure

Introduction to Quick Sort in Data Structure

Quick Sort in a data structure is a method to sort the list of elements. It uses the divide and conquer approach for this that means the array of elements are divided into 2 parts, and then further quick sort algorithm is applied to these 2 parts. This division of array takes place using a pivot point. The position of a pivot is selected such that the elements on the left of the pivot are less than the pivot element and also the element on the right is greater than the pivot element. This partitioning aims to obtain the sorted array in linear running time.

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Algorithm for Quick Sort in Data Structure

Any of the following methods can choose a pivot:

Last element of the array

The first element of the array

Any random element is picked.

Median is picked as a pivot.

Algorithm for Quick Sort:

swap myarr[i] and myarr[j] }

Explanation: In the above algorithm, there is pseudocode for partition function used to find the partition element of the array followed by pseudocode for quicksort. Quick Sort algorithm calls the partition function to calculate the partitioning point. Quick Sort is a tail-recursive, in-place algorithm that makes it suitable for use in case of arrays of a large number of elements.

Examples to Implement Quicksort in Data Structure

Quick Sort can be implemented using 2 below scenarios which are as follows:

1. Recursive version of Quick Sort

Here we will see the recursive version of quicksort.

Code:

pivot = mymyarr[right] myarr[i],myarr[j] = myarr[j],myarr[i] myarr[i+1],myarr[right] = myarr[right],myarr[i+1] myarr = [12,56,23,767,3,88,3,56,5] print (“%d” %myarr[i])

Output:

Code Explanation: The above program is for the recursive Quick Sort approach where myarr is defined to be sorted, and 0th element, i.e. 12 is considered to be starting index and n-1th element, i.e. 5 is the end index. A partition function is called to find the partitioning element. Here we are considering the pivot element to be the last element and index of a smaller element less than the left of the array being passed as an argument. Then each element is compared with pivot and in case element smaller than pivot is found I get incremented and swapping of an element occurs. And when no element is left to be swapped, all elements in the left are lesser than pivot and elements on the right are greater than the pivot.

Further quicksort algorithm is called for this subarray, and this way algorithm keeps on dividing the array and sort the elements.

Complexity

Here are 3 types of complexity which are explained below:

T(n) = 2T(n/2) + Θ(n)

Thus time complexity for the above expression is Θ(nLogn).

2. Worst Case: This case is said to occur if the partitioning element is always with the smallest or greatest array element. In such case following is the recurrence:

T(n) = T(0) + T(n-1) + Θ(n)

which is equivalent to,

T(n) = T(n-1) + Θ(n)

Thus complexity in such a case is said to be Θ (n2).

3. Average Case: Such a case occurs when the partition occurs when partitioning divides the elements such that O(n/9) elements are in one set and 9n/10 in other. Recurrence in such case is,

T(n) = T(n/9) + T(9n/10) + Θ(n)

The above algorithm needs some optimizations to reduce the complexity, such as taking pivot to be any random element or reciting the smaller array first and using the tail-recursive approach. Recursion requires a lot of space in the function call stack to store the left and right elements along with other parameters. Such a drawback can be avoided using the below iterative approach of QuickSort.

2. Iterative Version of Quick Sort

Here we will see the iterative version of quicksort.

Code:

x = myarr[right] myarr[i], myarr[j] = myarr[j], myarr[i] myarr[i + 1], myarr[right] = myarr[right], myarr[i + 1] right = stack[top] left = stack[top] myarr = [12,56,23,767,3,88,3,56,5] print (“% d” % myarr[i]),

Output:

Code Explanation: Partition function is the same in both the programs. Only the call to Sort the element changes as here an auxiliary stack is used to store the elements and pop out and store them in a sorted manner. To reduce the size of the stack being used, one must push the smaller stack first.

Conclusion

Quick Sort method sorts the elements using the Divide and Conquer approach and has an average O(nLogn) complexity. It can be implemented in both recursive and iterative way. It is in-place, cache-friendly and also a tail-recursive algorithm. It is mostly preferred in case of arrays as a lot of access to elements is required, which consumes a lot of time in case of linked lists.

Recommended Articles

This is a guide to Quick Sort in Data Structure. Here we discuss the introduction and algorithm for quick sort in a data structure and code implementation. You can also go through our other suggested articles to learn more –

## How To Use For In Statement To Loop Through An Array In Javascript

We use the chúng tôi statement of JavaScript for looping over enumerable properties of an array or object. It is a variety of for loops. Unlike other loop constructs in JavaScript, the chúng tôi loop doesn’t have to bother about the number of iterations. This is because the iteration size is fixed based on the enumerable properties of the object or the number of elements in the array.

The “for…in” statement in JavaScript

A chúng tôi loop iterates over all the enumerable properties of an object. All the properties that are assigned using a simple assignment operator or by default initializer are considered enumerable properties.

Syntax for(var num in numbers){ }

This creates a variable num that iterates over all the elements in the array numbers. This num takes on the index of the elements stored in the numbers array one by one.

Let’s see the working of chúng tôi loop with an example.

Example 1

Here we will create an array of strings and then iterate over it using chúng tôi loop. Let’s look at the code for same.

var

arr

=

[

“xyz”

,

“abc”

,

“pqr”

]

;

var

text

=

“”

;

for

(

var

str

in

arr

)

{

text

+=

arr

[

str

]

+

“,”

;

}

document

.

getElementById

(

“result”

)

.

innerHTML

=

text

;

In the above code, the str takes on values 0,1 and 2 respectively which is used for retrieving the elements of the array.

The chúng tôi loop though usable, works pretty well with objects rather than arrays. This is because the loop variable takes on the value of keys one by one making the iteration of the object pretty easy.

Syntax for(var num of numbers){ }

This creates a variable num that iterates over all the elements in the array numbers. This num takes on the value of the elements stored in the numbers array one by one.

Here’s an example of how to use chúng tôi loop with objects in JavaScript.

Example 2

Here we will create an array of elements containing different data types. we will use the chúng tôi loop to iterate over that array.

var

arr

=

[

“Jane Doe”

,

2

,

59.57

]

;

for

(

var

ele

of

arr

)

{

}

document

.

getElementById

(

“result”

)

.

innerHTML

=

text

;

In the above code, as is visible in the output as well, the variable ele takes on the value of the elements present in the array.

We can also use the Array.prototype.forEach() method for traversing the array. The argument of forEach() is a function that is executed for all the elements of the array.

Syntax const arr = ["Jane Doe", 2, 59.57] arr.forEach(function fun(ele){ }

Note that the “prototype” is replaced with the array’s name, which is arr in this case. The function fun has one argument ele which takes on the values of the elements stored in the array arr one by one.

Here’s an example of how to use the forEach() method with arrays in JavaScript.

Example 3

Here we will create an array of elements containing different data types. we will use the forEach() method to iterate over that array.

Let’s look at the code for the same.

var

arr

=

[

“Jane Doe”

,

2

,

59.57

]

;

arr

.

forEach

(

function

fun

(

ele

)

{

}

)

document

.

getElementById

(

“result”

)

.

innerHTML

=

text

;

In the above code, as is visible in the output as well, the variable ele takes on the value of the elements present in the array.

Conclusion

The chúng tôi chúng tôi and forEach() constructs make our life easier by providing much-needed variations of the conventional for a loop.

## Sort And Save Any Html Table Easily With Tabletools For Firefox

As an SEO, web marketer and blogger, I need to process tons of information daily. Very often this information is compiled in a table (I love organizing information in tables myself). Today I am reviewing a great FireFox addon that makes working with HTML tables easy and fun.

TableTools is the FireFox addon that lets you easily sort table, extract information from tables and copy tables. (For some reasons, the addon is not in the official addons directory but I am using it for some quite time and have never had any (security) issues with it).

HTML Table Sorting Options

Just install the addon, navigate to any web page containing an HTML table and try sorting it:

Find “Sort table column as…” in the context menu;

Select the format to sort by:

US time,

European Time;

Time;

Number/ Currency;

Alphabetically;

Auto-detect!

For example, the tool works like a charm on our SEO tools page – if you want to sort any of the feature-comparing tables (by presence / absence of any of the features):

Quoting the developer, sorting options and features include:

Sorts fast and accurate and even faster when reversing sorted column.

Automatically detects date, number, text, currency, IP address and sort them. Auto-detect timestamp (not just date), negative numbers, scientific notations, multiple currencies correctly.

Allows user to specify column data type explicitly through context menu.

Supports multiple tables on same html page.

Works with thead, tbody, th, etc. html tags. Or even nested tables. Allows multi-row header and footer.

Tolerates table colspans, although the end sorting results could be funny looking

Supports various levels of style preserving (row-level, cell-level or table-level (default)). Particularly useful for table rows that are alternatively highlighted (choose ‘row-level’ for it, which is default).

HTML Table Saving Options

Now, besides customizing the page right on the page, the tool also offers quite a few options that make extracting the information from the page much easier. You can:

Copy as tab-delimited text;

Copy as justified tab tab-delimited;

Copy as HTML;

Copy filtered rows as tab-delimited;

Copy filtered rows as justified tab-delimited;

Copy filtered rows as HTML:

From there you can:

Customize sorting behavior (to sort ascending first);

Set the time format;

Set the keyboard shortcuts;

etc:

All in all, the tool is an awesome time-saver and a must-have for people who regularly need to work with web pages (regardless of their profession). Enjoy!

## Substitute Random Items In A Javascript Array?

To substitute random items with items from an array with different ones in JavaScript. Let’s look at the instance; the array is −

Var array=[m,n,o,p]

Let’s choose two random items to be replaced with a, while the others remain in their original positions. If m and n are the randomly selected items, and one is removed on one instance, the array would be −

Changed array=[a,a,o,p]

Let’s dive into the article to learn more about substituting random items in a JavaScript array. To substitute random items, use random() along with map().

Using random() method

The JavaScript method random() is used to return a pseudo-random or random number that falls inside a specified range. The random() function must be called through the placeholder object Math because it is a static function of the Math object.

Syntax

Following is the syntax for random() −

Math.random(); Using map()

The map() method builds a new array from the contents of the calling array after performing a given function on each element.

Syntax

Following is the syntax for map() −

array.map(function(currentValue, index, arr), thisValue)

For getting more understanding on substituting a random item in a JavaScript let’s look into the following examples.

Example

In the following example we are running the script to substitute the random item in the JavaScript array.

function randomone(array, count) { return function() { const indices = new Set(); do { indices.add(Math.floor(Math.random() * array.length)); } while (indices.size < count) }; } var myArray = [‘A’, ‘B’, ‘C’, ‘D’], newarray = randomone(myArray, 2); document.write(…newarray());

When the script gets executed, it will generate an output consisting of an array with a value of “1” substituted randomly in between the array items. This will get changed whenever the user executes the script.

Example

Consider the following example, here we are running the script to get unique random indexes and running a loop over the indexes and making them equal to 2.

var my_arr = [“ab”, “bc”, “cd”, “de”]; const set = new Set(); while (set.size < count) { set.add(Math.floor(Math.random() * num)); } return […set]; }; const output = […arr]; return output; }; document.write(JSON.stringify(alter(my_arr)));

On running the above script, the output window will pop up, displaying the array generated with a value of “2” substituted randomly in the array by the event that triggers the script.

Example

Execute the below script to observe how to substitute random item in a JavaScript array.

function substituteRandomValue(names, size) { return function() { const index = new Set(); do { index.add(Math.floor(Math.random() * names.length)); } while (index.size < size) }; } var names = [‘John’, ‘David’, ‘Bob’, ‘Mike’, ‘Carol’, ‘Sam’], result = substituteRandomValue(names, 2);

hen the script gets executed, the event gets triggered and displays an array with a randomly substituted value in the indexes, and it will keep changing whenever the user executes the script.

## Golang Program To Append An Element Into An Array

In this tutorial, we will write a go language program to iterate over an array. An array is a data structure, which is used to store data at contiguous memory locations. There are many methods to append an element in an array. We shall discuss them in this program

Example 1: Add Values to an Array of Strings in the Main() Function

In this example, we will write a go language program to add values to an array of strings in the main() function. We will first initialize an array of strings of specific size and then add values to its every index

Algorithm

Step 1 − First, we need to import fmt package.

Step 2 − Now, start the main() function. Inside the main() initialize an array of strings.

Step 3 − In order to add values to this array we have to mention the index to which we wish to store a particular value.

Step 4 − So, mention the index after the name of the array and assign the value to that index using the equality operator

Step 5 − In the same way store values to every index of the array. then we need to print the array.

Step 6 − To print the array use fmt.Println() function and mention each index that should be printed.

Example package main import "fmt" func main() { var array [3]string array[0] = "India" array[1] = "Canada" array[2] = "Japan" fmt.Println("The first element of array is:", array[0]) fmt.Println("The second element of array is:", array[1]) fmt.Println("The third element of array is:", array[2]) } Output The first element of array is: India The second element of array is: Canada The third element of array is: Japan Example 2: Add Values to an Array of Strings using an Internal Function

In this example, we will write a go language program to add values to an array of strings using the append() function. The append is a library function in the go language that is used to add values to an array or a map.

Syntax func append(slice, element_1, element_2…, element_N) []T

The append function is used to add values to an array slice. It takes a number of arguments. The first argument is the array to which we wish to add the values followed by the values to add. The function then returns the final slice of an array containing all the values.

func make ([] type, size, capacity)

The make function in go language is used to create an array/map it accepts the type of variable to be created, its size, and capacity as arguments and returns the slice that we can store in the variable.

Algorithm

Step 1 − First, we need to import the fmt package.

Step 2 − Then, start the main() function. Inside the main() create an array of strings using the make() function.

Step 3 − Now, insert values to the array created above using the append() function.

Step 4 − The values are stored at respective indexes of the array starting from 0.

Step 5 − Now, we need to print the array on the screen for that use fmt.Println() function and print the value at each index.

Example package main import "fmt" func main() { array := make([]string, 0, 3) array = append(array, "Apple", "Mango", "Banana") fmt.Println("The first element of array is:", array[0]) fmt.Println("The second element of array is:", array[1]) fmt.Println("The third element of array is:", array[2]) } Output The first element of array is: Apple The second element of array is: Mango The third element of array is: Banana Example 3: To Add Values to an Array of Strings through a Different Array using Internal Functions

In this program, we will write a go language program to append values in an array of strings through a different array in the main() function. We will first initialize two arrays and then will store all the values of the second array in the first one.

Algorithm

Step 1 − First, we need to import the fmt package.

Step 2 − Then, start the main() function. Inside the main() create an array of strings using the make() function.

Step 3 − Now, insert values to the array created above using the append() function and print the array on the screen.

Step 4 − Similarly, create another array of string types and add values to it. Also, print the array on the screen.

Step 5 − Now, we need to add the values of the second array to the first array. for that use append() function.

Step 6 − The first argument to the function will be the array through which we wish to store values and the second argument will be the array through which we wish to store values

Step 7 − Now, we need to print the array on the screen for that use fmt.Println() function and print the value at each index.

Example package main import "fmt" func main() { array := make([]string, 0, 3) array = append(array, "Apple", "Mango", "Banana") fmt.Println("The first array is:", array) fmt.Println() array1 := make([]string, 0, 2) array1 = append(array1, "pine-apple", "cherry") fmt.Println("The second array is:", array1) array = append(array, array1...) fmt.Println() fmt.Println("The new array thus formed by combining the two arrays is:") for i := 0; i < 5; i++ { fmt.Println(array[i]) } } Output The first array is: [Apple Mango Banana] The second array is: [pine-apple cherry] The new array thus formed by combining the two arrays is: Apple Mango Banana pine-apple cherry Conclusion

We have successfully compiled and executed a go language program to append values to an array along with examples. In the first program, we used the equality operator to add values at respective indexes, and in the second and third programs, we used a library function called append() to achieve the result.

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