**Creating and Working with Queues**
A queue is a fundamental data structure that follows the First-In-First-Out (FIFO) principle, where elements are added to the end of the queue and removed from the front. In this article, we will explore how to create and work with queues using JavaScript.
**Basic Queue Operations**
To create a basic queue, we can use an array to store the elements. We can add elements to the queue by using the `enqueue` function, which takes two arguments: the element to be added and its priority (if applicable). For example, if we want to enqueue an item with priority 5, we would pass in an array `[item, 5]`. The `enqueue` function returns the updated queue.
Once we have added elements to the queue, we can retrieve them using the `dequeue` function. This function removes and returns the element at the front of the queue. If we want to print all elements in the queue without removing them, we can use the `dq` function, which simply prints the elements at the beginning of the array.
For example, if we have a queue with `[a, b, c]`, calling `dequeue` would return `a`, and then calling `dq` again would print the remaining elements: `[b, c]`.
**Priority Queues**
A priority queue is similar to a basic queue but adds an additional layer of complexity through prioritization. When enqueueing an item into a priority queue, we also pass its priority as a second argument. This allows us to determine the order in which items are added to the queue.
For example, if we want to enqueue two items with different priorities, we would pass in arrays `[item1, priority1]` and `[item2, priority2]`. The item with the higher priority will be added to the front of the queue, while items with lower priorities will be added after them.
However, when printing elements from a priority queue, the order is determined by their priority. If two or more items have the same priority, they are printed in the order they were originally enqueued.
**Priority Queue Implementation**
To implement a priority queue in JavaScript, we can use an array to store the elements and their priorities. We can add elements to the queue using the `enqueue` function, which checks the priority of each element as it is added to determine its position in the queue.
Here's an example implementation:
```javascript
function pq(element) {
if (queue.length === 0 || element[1] > queue[0][1]) {
queue.push(element);
} else {
for (let i = 0; i < queue.length; i++) {
if (element[1] > queue[i][1]) {
break;
}
}
queue.splice(i, 0, element);
}
}
function dequeue() {
const removedElement = queue.shift();
return removedElement;
}
function printQueue() {
console.log(queue.map((item) => item[0]));
}
```
In this implementation, the `pq` function adds an element to the queue while maintaining the priority order. The `dequeue` function removes and returns the front element of the queue, and the `printQueue` function prints all elements in the queue without removing them.
**Example Usage**
Here's an example usage of the priority queue implementation:
```javascript
const queue = [];
pq([1, 5]);
pq([2, 3]);
pq([3, 5]); // same priority, so order is preserved
printQueue(); // prints: [1, 2]
dequeue();
printQueue(); // prints: [2, 3]
```
In this example, we create an empty queue and enqueue three elements with different priorities. We then print the entire queue to see the order of the elements based on their priority. Finally, we dequeue an element from the front of the queue and print it again to demonstrate that the remaining elements are in the correct order.
Overall, queues provide a fundamental data structure for implementing algorithms and solving problems in programming. By understanding how to create and work with queues, developers can build efficient and effective solutions to a wide range of applications.