A look at the queue data structure
A queue is a list — similar to the real world queue. The one who gets into the queue first is the one who is removed first from the queue.
Technically speaking, this process is called first in, first out (FIFO). The element which is inserted first will be removed first from the list
Elements are always added to the end of the list and removed from the front of the list.
Different operations in Queue are:
-
Enqueue→ Add an element to the queue -
Dequeue→ Remove an element from the queue
Operations we are going to implement:
- Inserting an element at the end of the queue
- Deleting an element in the front from the queue
- Get the front element
- Get the Last element
- Check if a queue is empty
- Print the elements of the queue
- Print the length of the queue
Let’s create a Queue class.
class Queue {
constructor(){
this.data = [];
this.rear = 0;
this.size = 10;
}
}
data → is the list in which we store our elements
rear → is used to store the position in which the next element will be stored
size → maximum number of elements a queue can have
Enqueue: Inserting an Element at the End of the Queue
After inserting an element to the queue, we need to increase the rear value by 1 so the rear points to the next position where the new element will be inserted.
enqueue(element) {
this.data[this.rear] = element;
this.rear = this.rear + 1;
}
In addition to the above case, we need to check if the queue is full or not so it avoids overflow.
enqueue(element) {
if(this.rear < this.size ) {
this.data[this.rear] = element;
this.rear = this.rear + 1;
}
}
Length: Returns the Length of the Queue
To get the length of the queue, we can use the rear attribute.
length() {
return this.rear;
}
IsEmpty: Check If the Queue Is Empty
If the rear points to 0 , then we can say that the queue is empty. Because the rear points to the position where the new element will be placed, if the rear points to 0, there’s no element in the queue
isEmpty() {
return this.rear === 0;
}
GetFront: Get the Front Element of the Queue
In addition to getting the front element, this will check if the queue is empty or not.
getFront() {
if(this.isEmpty() === false) {
return this.data[0];
}
}
GetLast: Get the Last Element Added to the Queue
We know the rear value points the new position, where the next element will be inserted into the queue. So to get the last element in the queue, we can decrease the rear index by 1.
getLast() {
if(this.isEmpty() === false) {
return this.data[ this.rear - 1 ] ;
}
}
Delete: Deleting the Front Element From the Queue
The element which is inserted first is the one that is deleted first. So we can delete the front element and decrease the rear value by 1 so the rear points to the next position to insert correctly.
dequeue() {
if(this.isEmpty() === false) {
this.rear = this.rear-1;
return this.data.shift();
}
}
Print Elements of the Queue
We can print the elements of the queue from the0 index to the rear-1 index of the queue.
print() {
for(let i =0; i < this.rear; i++) {
console.log(this.data[i]);
}
}
Reset Queue
Delete all elements of the queue and set the rear to 0.
clear() {
this.data.length = 0;
this.rear = 0;
}
The End
Let’s combine all the above code together
https://gist.github.com/Jagathishrex/d6c9b4688b9f996ca0c49a90ead09f08#file-queue-js
Thanks for reading. I hope you enjoyed the article.
Js Jeep 🚙 