# DS with JS — Stack & Queue

## Data Structures with JavaScript — Chapter Three — Stacks and Queues

❗️All the code snippets you will see below are just Pseudo code. If you want to see working code — click here

# Prerequisites

Before proceeding further, make sure you have gone through both of these posts first because I am using Linked Lists to implement Stack and Queue rather than Arrays.

**Why to use Linked Lists while implementing Stacks and Queues ?**

I found some lines over this —

…because linked lists store data elements in linear sequences, they can be used to give alternative implementations of stacks and queues. One advantage to using linked lists is that we don’t have to worry about filling up something like an array — we can just keep allocating cells as long as we need to (unless we run out of memory). Implementing a stack using a linked list is particularly easy because all accesses to a stack are at the top. One end of a linked list, the beginning, is always directly accessible. We should therefore arrange the elements so that the top element of the stack is at the beginning of the linked list, and the bottom element of the stack is at the end of the linked list. We can represent an empty stack with null…

another reason is that you will able to practice linked-lists while implementing stacks and queues which will give you the understanding of how Stacks and Queues works while making you strong with linked-lists.

*read full article over **here**..*

# Lets’ begin!!

# Core

# ⚜️ The list

- Push
- Pop
- Peek
- Reverse
- Length
- Search
- IsEmpty
- Traverse

Lets do some code now…

## 🔅 Push

**push**( **item** )**{**

**let** node **=** **new** Node( item )

**if**( **this**.top ) {

node.next **=** **this**.top

**this**.top **=** node

} **else** {

**this**.top **=** node

}

**}**

## 🔅 Pop

**pop**() **{**

**if**( **this**.top ) {

**let** itemToPop **=** **this**.top

**this**.top **=** **this**.top.next

**return** itemToPop.data

} **else** {

log('Stack is empty!')

**return** **false**;

}

**}**

## 🔅 Peek

**peek**() **{**

**if**( **this**.top ) {

**return** **this**.top.data

} **else** {

**return null**

}

**}**

## 🔅 Reverse

**reverse**() **{**

**let** current **=** **this**.top

**let** prev **=** *null*;

**while**( current ) {

**let** next **=** current.next

current.next **=** prev

prev **=** current

current **=** next

}

**this**.top **=** prev

**}**

⚠️ It is same as reversing a Singly-Linked List

## 🔅 Length, Search & IsEmpty

length(){

letcurrent=this.top

letcounter=0

while( current ) {

counter++

current=current.next

}

returncounter}search(item){

letcurrent=this.top

while( current ) {

if( current.data===item )returntrue

current=current.next

}

returnfalse}isEmpty(){

returnthis.length>1}

## 🔅 Traverse

**traverse**( **fn** ) **{**

**let** current **=** this.top

**while**( current ) {

fn( current )

current **=** current.next

}

**}**

# Core

# ⚜️ The list

- Enqueue
- Dequeue
- Length
- Peek
- IsEmpty
- Traverse

## 🔅 Enqueue

enqueue(item){

letnode=newNode( item )if( !this.head ) {

this.head=node

this.tail=node

}else{

this.tail.next=node

this.tail=node

}}

## 🔅 Dequeue

**dequeue**() **{**

**if**( !**this**.head ) {

**return** 'No item'

} **else** {

**let** itemToPop **=** **this**.head

**this**.head **=** **this**.head.next

**return** itemToPop

}

**}**

## 🔅 Length, Peek & IsEmpty

length(){

letcurrent, counter

[ current, counter ]=[this.head, 0 ]

while( current ) {

counter++

current=current.next

}

returncounter}peek(){

if(this.head ) {

returnthis.head.data

}else{

return'Empty'

}}isEmpty(){

returnthis.length()<1}

## 🔅 Traverse

**traverse**( fn ) **{**

**let** current **=** **this**.head

**while**( current ) {

fn( current )

current **=** current.next

}

**}**

You can implement any operation over these stacks and queues which you can implement using Linked Lists.

# Practice

- Hackerrank —
*Data Structures*

# Last important thing…

# About this post

This post is the third instalment to its series “**DS with JS**”. There will be more in this series. Next will be on **next Monday Morning**. **Stay tuned!**

# That’s It

## Happy Coding !!

🎧Listening to “Touch — Matia Cupelli” . Sadness, broken heart, piano & dreams.. only thing missing is — this music…

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