A queue uses FIFO (first-in-first-out) ordering, that is, items are removed from the queue in the same order that they are added, like a line. Queues can be used whenever is necessary to process things in that order (FIFO), like requests to a single shared resource, CPU scheduling, also helps in algorithms of other data structures, such as breadth-first search in graphs.

Representation

A queue can be implemented using an array or a linked list, can be either fixed or dynamic size.

Basic operations

• Add - Add an item to the end of the queue, also called enqueue.
• Remove - Remove the first item from the queue, also called dequeue.
• Peek - Return the top of the queue, without removing it.
• isEmpty - Return true if the queue is empty.
• isFull - Return true if the stack is full, used when the queue is fixed size.

Here's an implementation of a queue using an array, in TypeScript an array doesn't have a fixed length, so the operation isFull is not required, however, you can implement a queue with a fixed length and use that operation.

1class Queue<T> {
2  private array: T[] = [];
3
4  add(data: T): void {
5    this.array.push(data);
6  }
7
8  remove(): T | undefined {
9    if (this.isEmpty()) throw new EmptyQueueException();
10
11    return this.array.shift();
12  }
13
14  peek(): T {
15    if (this.isEmpty()) throw new EmptyQueueException();
16
17    return this.array[0];
18  }
19
20  isEmpty(): boolean {
21    return this.array.length === 0;
22  }
23}