Data Structures & Algorithms in JavaScript(Stack)

Data Structures & Algorithms in JavaScript(Stack)

Hello Everyone, This is part 2 in the series of blogs about data structure and algorithms in JavaScript. Previously I have explained Array. In this blog, I will cover Stack. 

What is Stack?

Stack is a linear data structure which follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). – geeksforgeeks.org

Real World eg. of the stack can be a pile of books, where books are placed one above another, books can be added or remove from the top of the pile of books

List Of Operations Available

  • Push: Insert an element in the stack.
  • Pop: Remove an element from the stack.
  • Peek: Return the top element of the stack.
  • Size: Return Size of the stack.
  • isEmpty: Check if the stack is empty if empty return true else false.
  • Clear: Reset the stack.

Implementation of Stack in JavaScript

There are two ways in which stack can implement in javascript one way by using Array or using javascript object. As Array already has a push method to insert an element at end of the array, a pop method to remove an element, to get the length of the array it has a property length which returns the size of the array if the length is equal to zero then the array is empty. you can get the array implementation of the Stack here

Implementation of Stack using JavaScript Objects

let’s define ES6 class name Stack, with two properties, count which will keep track of the number of elements in the stack and items, an object which will store the elements. Items object key will be incremental count property and value as the element store in it.


class Stack {
    constructor() {
        this.count = 0;
        this.items = {};
    }
}

Push

To add an element to the stack we will use the count property as key for the items object & element as value. After pushing the element in the stack we will increment the count property by one. we can only add new items to the top of the stack, meaning at the end of the stack


 push(element) {
        this.items[this.count] = element;
        this.count++;
    }

Pop

While removing an element from the stack, there two cases:

  1. If the stack is empty, return undefined
  2. If the stack is not empty
    • Store the value of the top element i.e (count -1)
    • decrement the count property by one
    • delete element from items object and return the stored value.

As the stack uses the LIFO principle, the last item that we added is the one that is removed


   pop() {
        if (this.isEmpty()) {
            return undefined;
        }
        let result = this.items[this.count-1];
        this.count --;
        delete this.items[this.count];

        return result;
    }

Peek

If the stack is empty, return undefined else return  Top element i.e (count -1)


  peek() {

        if (this.isEmpty()) {
            return undefined;
        }
        return this.items[this.count-1];
    }

Size

Return count property, which keeps track of the number of elements in the stack.


size() {
        return this.count;
    }

isEmpty 

Return boolean , if the count property is zero then yes true else false.

isEmpty() {
        return this.count == 0;
    }

Clear

We can reset it to the same value as we define in the class constructor method.

 clear() {
    this.items = {};
    this.count = 0;
    return this.items;
    }

Or we could also pop an element from the Stack until it’s empty.

while (!this.isEmpty()) {
this.pop();
}

you can get the full source here

Conclusion :

A stack is a data structure that uses the LIFO (Last In First Out ) principle. We can insert or remove an element from the top of the stack only

Stacks have a variety of applications in real-world problems. They can be used for backtracking problems to remember tasks or paths visited, and to undo actions.

MethodsComplexity
popO(1)
pushO(1)
peekO(1)
Complexity of the Stack Methods

So, stay tuned for the next blog, in which I will cover another DS Queue.

Swarup Das

Swarup Das

Web Developer, Tech Enthusiast. Passionate about new technology and programming languages.

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