theprimeagen / fem-algos Goto Github PK

First of all, this is a great course (still working through it...).

One thing that really tripped me off is the Queue.enque() method:

type Node<T> = {
    value: T;
    next?: Node<T>;
}

export default class Queue<T> {
    public length: number;
    private head?: Node<T>;
    private tail?: Node<T>;

    constructor() {
        this.head = this.tail = undefined;
        this.length = 0;
    }

    enqueue(item: T): void {
        const newNode = {value: item} as Node<T>;
        this.length++;
        if (!this.tail) {
            this.tail = this.head = newNode;
            return;
        }
        this.tail.next = newNode;
        this.tail = newNode;        
    }

    deque(): T | undefined {
        if (!this.head) {
            return undefined;
        }
        this.length--;

        const head = this.head;
        this.head = this.head.next;

        if (this.length === 0) {
            this.tail = undefined;
        }

        return head.value;
    }
    peek(): T | undefined {
        return this.head?.value;
    }   
}   

The confusing part is these two lines:

this.tail.next = newNode;
this.tail = newNode; 

This doesn't have the effect as explained in the video lecture (first point the element at this.tail.next to the new node and then set this.tail to the same node). The second line - this.tail = newNode - has as the effect that this.tail.next is always undefined (upon returning from the method).

But in one very special case, when this.tail and this.head point to the same Node object (the line: this.tail = this.head = newNode; in the if-condition) it does affect the this.head.next.

I still have trouble comprehending this implementation w/o using a debugger. Has someone found a less obscrure implementation?

Link on the website points to

https://frontendmasters.com/course/algorithms/

but it should be

https://frontendmasters.com/courses/algorithms/

D:

In your lesson on queues you mention that it is mind-boggling that deque is spelled this way, but as a method to remove an item from a queue, it actually should be spelled dequeue as you surmised.

Deque would be pronounced "deck" and refers to a double-ended queue data type.

https://en.wikipedia.org/wiki/Double-ended_queue