/**

* @author Rashik Ansar

*

* Implemtaion of Stack data structure

* Stack follows LIFO (Last In First Out) priniciple

* For Insertion and Deletion its complexity is O(1)

* For Accessing and Searching its complexity is O(n)

*/

class Stack {

/**

* initialize stack instances with null

*/

constructor() {

this.first = null;

this.last = null;

this.size = 0;

}

/**

* Adding data to Top of the stack

* @param {*} data

* @returns {Stack}

*/

push(data) {

let newNode = new Node(data);

if (!this.first) {

this.first = newNode;

this.last = newNode;

} else {

let temp = this.first;

this.first = newNode;

this.first.next = temp;

}

this.size++;

return this;

}

/**

* Removing data frpm Top of the stack

* @returns {Node.data} The data that is removing from the stack

*/

pop() {

if (!this.first) {

throw Error('UNDERFLOW :::: Stack is empty, there is nothing to remove');

}

let current = this.first;

if (this.first === this.last) {

this.last = null;

}

this.first = current.next;

this.size--;

return current.data;

}

/**

* @returns {Node.data} Top most element of the stack

*/

peek() {

if (!this.first) {

throw Error('Stack is empty');

}

return this.first.data;

}

}

class Node {

constructor(data) {

this.data = data;

this.next = null;

}

}