DS with JS — Linked Lists
Data Structures with JavaScript — Chapter One — Linked Lists
Introduction
A Linked List is a linear collection of data elements, called nodes, pointing to the neighbouring node by means of pointer.
Under the simplest form, each node is composed of data and a reference (in other words, a link) to the next node or previous node in the sequence.
⚠️ If you wan’t to learn more about linked-lists click here because in this post I will not cover the theoretical concepts about linked-list. I will just go straight into coding.
Core
The most important part of a linked list is a node. It consist of two things —
- Data
- Pointers
In Single Linked Lists there is only one pointer (next ) but in Double Linked lists there are two pointers (prev & next ). There can be more than two pointers also. It totally depends on your purpose of creating them.
Whenever we create an instance of our LinkedList
class, the constructor
executes and it create a head
node with both data and next as null
. Then we use its append
method to insert items into this list. In this post, we will go through the following methods/operations on Linked Lists —
⚜️ The list
- Append
- AppendAt
- Remove
- RemoveAt
- Reverse
- Swap
- IsEmpty & Length
- Traverse
- Display
- Search
and a lot more… So, without further ado…
Lets’ begin!!
❗️All the code snippets you will see below are just Pseudo code. If you want to see working code — click here
🔅 Append
append( item ) {
let current = this.head;
let newNode = new Node(item)
while( current.next !== null ) {
current = current.next
}
current.next = newNode;
return true;
}
🔅 AppendAt
appendAt( pos, item ) {
let counter = 0;
let current = this.head;
let newNode = new Node(item);
while( current.next !== null ) {
if( counter === pos ){
newNode.next = current.next
current.next = newNode
return true;
}
current = current.next
counter++;
}
return false;
}
🔅 Remove
remove( item ) {
let current = this.head;
while( current !== null ) {
let previous = current;
current = current.next;
if( current.data === item ) {
previous.next = current.next;
return true;
}
}
return false;
}
🔅 RemoveAt
removeAt( pos ) {
let counter = 0;
let current = this.head;
while( current !== null ) {
let previous = current;
current = current.next
if( counter === pos ){
previous.next = current.next;
return true;
}
counter++;
}
return false;
}
🔅 Reverse
reverse() {
let current = this.head.next;
let prev = null;
let next;
while(current !== null) {
next = current.next
current.next = prev
prev = current
current = next
}
this.head.next = prev
return true
}
It is easy to understand what we see instead of what we read. So, If the mechanism of this reverse
function is still unclear to you, I have made a gif
in order to show you how the execution goes.
🔅 Swap
swap( nodeOne, nodeTwo ) {
let current = this.head;
let counter = 0;
let firstNode;
while( current !== null ) {
current = current.next;
if( counter == nodeOne ){
firstNode = current;
} else if( counter == nodeTwo ) {
let temp = current.data;
current.data = firstNode.data;
firstNode.data = temp;
}
counter++;
}
return true
}
🔅 isEmpty & Length
length() {
let current = this.head;
let counter = 0;
while( current.next !== null ) {
current = current.next
counter++;
}
return counter;
}isEmpty() {
return this.length() < 1
}
🔅 Traverse
If you want to execute a function over each node, then you can use traverse
. Just pass the function as shown in the example —
traverse( fn ) {
let current = this.head;
while( current.next !== null ) {
fn(current)
current = current.next;
}
return true;
}
🔅 Display
display() {
let current = this.head;
let elements = [];
while( current !== null ) {
elements.push( current.data );
current = current.next
}
return elements.join(" ");
}
🔅 Search
search( item ) {
let current = this.head.next;
let counter = 0; while( current ) {
if( current.data == item ) {
return counter
}
current = current.next
counter++
}
return false;
}
There are still a lot of things that we can do with linked-lists. Never stop doing practice. Explore yourself and think of problems by yourself. The more you think of problems — the more you brain will create links with Data Structures. Just keep checking DSwithJS Github repository for more.
Practice
- Hackerrank Data Structures — Linked Lists
- GeekForGeeks Data Structures
- LeetCode Linked Lists
One more important thing…
About this post
This post is the first of its series “DS with JS”. There will be more in this series. Next will be on next Monday Morning at 08:00 AM (UTC+05:30). Stay tuned!
That’s It
Happy Coding !!
🎧 Listening to “Just a dream…” . Great music for those who are motivated and dreaming about how their life is going to be change soon — Like me :)
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