Implementation of Queue in Javascript
In This article, we would be implementing Queue data structure in javascript. A Queue works on the FIFO(First in First Out) principle. Hence, it performs two basic operations that is addition of elements at the end of the queue and removal of elements from the front of the queue. Like Stack, Queue is also a linear data structure.
Note: Assuming a queue can grow dynamically we are not considering the overflow condition
Now let’s see an example of queue class using an array:-
Example:
// Queue class class Queue { // Array is used to implement a Queue constructor() { this .items = []; } // Functions to be implemented // enqueue(item) // dequeue() // front() // isEmpty() // printQueue() } |
As in the above definition we have created a skeleton of a queue class which contains a constructor in which we declare an array to implement queue. Hence, with the creation of an object of a queue class this constructor would be called automatically and the array will be declared
Let’s implement each of these functions:
- enqueue() – Adds an element to the queue
// enqueue function
enqueue(element)
{
// adding element to the queue
this
.items.push(element);
}
This function adds an element at the rear of a queue. We have used push() method of array to add an element at the end of the queue.
- dequeue() – Removes an element from the queue
// dequeue function
dequeue()
{
// removing element from the queue
// returns underflow when called
// on empty queue
if
(
this
.isEmpty())
return
"Underflow"
;
return
this
.items.shift();
}
This function removes an element from the front of a queue . We have used shift method of an array to remove an element from the queue.
- front() – returns the front element of the queue
// front function
front()
{
// returns the Front element of
// the queue without removing it.
if
(
this
.isEmpty())
return
"No elements in Queue"
;
return
this
.items[
0
];
}
This function returns the front element of the queue. We simply return the 0th element of an array to get the front of a queue.
Helper Methods
Let’s declare some helper method which is quite useful while working with the queue.
- isEmpty() – Returns true if the queue is empty
// isEmpty function
isEmpty()
{
// return true if the queue is empty.
return
this
.items.length ==
0
;
}
In this function we have used the length property of an array and if the array length is 0 then the queue is empty.
- printQueue()– Returns all the elements of an queue.
// printQueue function
printQueue()
{
var str =
""
;
for
(var i =
0
; i <
this
.items.length; i++)
str +=
this
.items[i] +
" "
;
return
str;
}
In this method we concatenate all the elements of the queue in a string and return the string
Note: Different helper method can be declared in Queue class as per the requirement.
Implementation
Now let’s use the queue class and its different method described above
// creating object for queue class var queue = new Queue(); // Testing dequeue and pop on an empty queue // returns Underflow console.log(queue.dequeue()); // returns true console.log(queue.isEmpty()); // Adding elements to the queue // queue contains [10, 20, 30, 40, 50] queue.enqueue( 10 ); queue.enqueue( 20 ); queue.enqueue( 30 ); queue.enqueue( 40 ); queue.enqueue( 50 ); queue.enqueue( 60 ); // returns 10 console.log(queue.front()); // removes 10 from the queue // queue contains [20, 30, 40, 50, 60] console.log(queue.dequeue()); // returns 20 console.log(queue.front()); // removes 20 // queue contains [30, 40, 50, 60] console.log(queue.dequeue()); // printing the elements of the queue // prints [30, 40, 50, 60] console.log(queue.printQueue()); |
Now once we are done with the implementation of Queue class we can use it different applications.
Application : An Interesting Method to Generate Binary Numbers from 1 to n
In this problem we generate different binary numbers from 1 to n.
// function to generate binary numbers function generatePrintBinary(n) { // Create an empty queue of strings var q = new Queue(); // Enqueue the first binary number q.enqueue( "1" ); // This loops is like BFS of a tree with 1 as root // 0 as left child and 1 as right child and so on while (n-- > 0 ) { // print the front of queue var s1 = q.front(); q.dequeue(); console.log(s1); // Store s1 before changing it var s2 = s1; // Append "0" to s1 and enqueue it q.enqueue(s1 + "0" ); // Append "1" to s2 and enqueue it. Note that s2 contains // the previous front q.enqueue(s2 + "1" ); } } // calling the above function // prints [1 10 11 100 101] generatePrintBinary( 5 ); |
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