Queues
What are queues?
- The queues are First in First out (FIFO) data structures
- Its the opposite of stacks
- The printer is the best example of a queue
Doubly ended queues
Its a data structure which is both First in First out (FIFO), and Last in Last out (LILO)
Write a code
Let’s implement a queue in Javascript
// Queue in Javascript
class Node {
constructor(data) {
this.data = data;
this.next = null;
}
}
class Queue {
constructor() {
this.first = null;
this.last = null;
this.length = 0;
}
enqueue(data) {
const newNode = new Node(data);
if (this.length === 0) {
this.first = newNode;
this.last = newNode;
} else {
this.last.next = newNode;
this.last = newNode;
}
this.length++;
return this;
}
dequeue() {
if (!this.first) {
return null;
}
if (this.first === this.last) {
this.last = null;
}
const holdingPointer = this.first;
this.first = this.first.next;
this.length--;
return this;
}
//isEmpty;
}
const queueInstance = new Queue();
queueInstance.enqueue('John');
console.log(queueInstance);
queueInstance.enqueue('Stark');
console.log(queueInstance);
queueInstance.dequeue();
console.log(queueInstance);
queueInstance.dequeue();
console.log(queueInstance);
// Output
// Queue {
// first: Node { data: 'John', next: null },
// last: Node { data: 'John', next: null },
// length: 1
// }
// Queue {
// first: Node { data: 'John', next: Node { data: 'Stark', next: null } },
// last: Node { data: 'Stark', next: null },
// length: 2
// }
// Queue {
// first: Node { data: 'Stark', next: null },
// last: Node { data: 'Stark', next: null },
// length: 1
// }
// Queue { first: null, last: null, length: 0 }