JavaScript Data Structures: Queue: Recap

Intro

Last time, we added the dequeue method.

I hope you learned something about the concept of a Queue and tried your best to implement it on your own.

Thoughts about the Queue 💭

We implemented the Queue using a Singly Linked List.

The Queue data structure is a very important concept, because we use it all the time.

The Queue is based on the "First In, First Out"-Principle, meaning the first node that goes into the queue will later be the first node, that goes out of the queue.

Examples in real life: people who want to pay in a store, the tasks of a printer.

• Access: O(N)
• Search: O(N)
• Insert: O(1)
• Remove: O(1)

Final Implementation 📝

Our Queue has these methods:

• enqueue, to add a node to the end of the queue
• dequeue, to remove a node from the start of the queue

class Node { constructor(value) { this.value = value; this.next = null; } } class Queue { constructor() { this.length = 0; this.start = null; this.end = null; } enqueue(value) { const newNode = new Node(value); if (!this.length) { this.start = newNode; this.end = newNode; } else { this.end.next = newNode; this.end = newNode; } this.length += 1; return newNode; } dequeue() { if (!this.length) { return null; } else { const nodeToRemove = this.start; this.start = this.start.next; nodeToRemove.next = null; if (this.length === 1) { this.end = null; } this.length -= 1; return nodeToRemove; } } } 

Further Reading 📖

• Wikipedia: Queue
• Wikibooks: Queue
• Wikipedia: FIFO

Questions ❔

• Can you implement a new method peek, that returns the start node, without removing it?

Next Part ➡️

We will compare the Data Structures we've built so far.

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