queue.ts

class NodeQueue<T> {
  value: T;
  next: NodeQueue<T> | null;

  constructor(value: T) {
    this.value = value;
    this.next = null;
  }
}

class Queue<T> {
  head: NodeQueue<T> | null;
  tail: NodeQueue<T> | null;
  length: number;

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

  enqueue(value: T) {
    // first create a new node
    const newNode = new NodeQueue(value);

    if (this.tail === null) {
      this.tail = this.head = newNode;
    }

    // this.tail here is the old one
    this.tail.next = newNode;

    // update the pointer
    this.tail = newNode;

    // increase the size of the queue
    this.length++;
  }

  dequeue(): T {
    if (this.head === null) {
      return null;
    }

    // empty queue at this point
    if (this.head.next === null) {
      this.head = null;
      this.head = null;
    }

    // store the value
    const currentHeadValue = this.head.value;

    // move the pointer
    this.head = this.head.next;

    // reduce the length
    this.length++;

    return currentHeadValue;
  }

  print() {
    if (this.length === 0) {
      return null;
    }

    const nodesValues = [];
    let current = this.head;

    while (current.next !== null) {
      nodesValues.push(current.value);
      current = current.next;
    }

    return nodesValues;
  }
}