Coding Challenge Practice - Question 86

The task is to implement a Queue by using Stack.

The boilerplate code

class Queue {
  enqueue(element) { 
    // add new element to the rare
  }
  peek() { 
    // get the head element
  }
  size() { 
    // return count of element
  }
  dequeue() {
    // remove the head element
  }
}

A Queue follows the First In, First Out rule.

Create an array that stores all the queue elements, and a pointer that points to the front of the queue.

this.items = [];
this.head = 0;

To add an element to the end of the queue

enqueue(element) {
  this.items.push(element);
}

To get the front element

peek() {
  return this.size() === 0 ? undefined : this.items[this.head];
}

To know how many valid elements are in the queue

size() {
  return this.items.length - this.head;
}

To remove the front element

dequeue() {
  if (this.size() === 0) return undefined;

  const value = this.items[this.head];
  this.head++;

  return value;
}

Dequeue stores the front value, moves the pointer forward and returns the removed value. If the queue is empty, undefined is returned.

The final code

class Queue {
  constructor() {
    this.items = [];
    this.head = 0;
  }
  enqueue(element) { 
    // add new element to the rare
    this.items.push(element);
  }
  peek() { 
    // get the head element
    return this.size() === 0 ? undefined : this.items[this.head];
  }
  size() { 
    // return count of element
    return this.items.length - this.head;
  }
  dequeue() {
    // remove the head element
    if(this.size() === 0) return undefined;

    const value = this.items[this.head];
    this.head++

    if(this.head >  50 && this.head * 2 >= this.items.length) {
      this.items = this.items.slice(this.head);
      this.head = 0;
    }
    return value;
  }
}

That's all folks!