class Node {
constructor(value){
this.value = value;
this.next = null;
}
}
class Stack {
constructor(){
this.top = null;
this.bottom = null;
this.length = 0;
}
peek() {
return this.top;
}
push(value){
const newNode = new Node(value);
if (this.length === 0) {
this.top = newNode;
this.bottom = newNode;
} else {
const holdingPointer = this.top;
this.top = newNode;
this.top.next = holdingPointer;
}
this.length++;
return this;
}
pop(){
if (!this.top) {
return null;
}
if (this.top === this.bottom) {
this.bottom = null;
}
const holdingPointer = this.top;
this.top = this.top.next;
this.length--;
return this;
}
//isEmpty
}
const myStack = new Stack();
myStack.peek();
myStack.push('google');
myStack.push('udemy');
myStack.push('discord');
myStack.peek();
myStack.pop();
myStack.pop();
myStack.pop();
//Discord
//Udemy
//google
// with arrays
class Stack {
constructor(){
this.array = [];
}
peek() {
return this.array[this.array.length-1];
}
push(value){
this.array.push(value);
return this;
}
pop(){
this.array.pop();
return this;
}
}
const myStack = new Stack();
myStack.peek();
myStack.push('google');
myStack.push('udemy');
myStack.push('discord');
myStack.peek();
myStack.pop();
myStack.pop();
myStack.pop();
//Discord
//Udemy
//google
// Queue implementation
class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}
class Queue {
constructor(){
this.first = null;
this.last = null;
this.length = 0;
}
peek() {
return this.first;
}
enqueue(value){
const newNode = new Node(value);
if (this.length === 0) {
this.first = newNode;
this.last = newNode;
} else {
this.last.next = newNode;
this.last = newNode;
}
this.length++;
return this;
}
dequeue(){
if (!this.first) {
return null;
}
if (this.first === this.last) {
this.last = null;
}
const holdingPointer = this.first;
this.first = this.first.next;
this.length--;
return this;
}
//isEmpty;
}
const myQueue = new Queue();
myQueue.peek();
myQueue.enqueue('Joy');
myQueue.enqueue('Matt');
myQueue.enqueue('Pavel');
myQueue.peek();
myQueue.dequeue();
myQueue.dequeue();
myQueue.dequeue();
myQueue.peek();
// Common interview question
// Implement Queue using Stacks
class CrazyQueue {
constructor() {
this.first = [];
this.last = [];
}
enqueue(value) {
const length = this.first.length;
for (let i = 0; i < length; i++) {
this.last.push(this.first.pop());
}
this.last.push(value);
return this;
}
dequeue() {
const length = this.last.length;
for (let i = 0; i < length; i++) {
this.first.push(this.last.pop());
}
this.first.pop();
return this;
}
peek() {
if (this.last.length > 0) {
return this.last[0];
}
return this.first[this.first.length - 1];
}
}
const myQueue = new CrazyQueue();
myQueue.peek();
myQueue.enqueue('Joy');
myQueue.enqueue('Matt');
myQueue.enqueue('Pavel');
myQueue.peek();
myQueue.dequeue();
myQueue.dequeue();
myQueue.dequeue();
myQueue.peek();
