README
priority-queue
functional, data oriented priority queue that doesn't suck
There are many priority queue implementations on the web, but I couldn't find any that meet these critera:
- does not allocate memory at run time
- has tests
- is functional, data oriented
- is tiny! (~150 lines of code)
- is a pure ES module
So here we are!
Usage
import PQ from 'priority-queue'
// declarea a custom function for comparing the priority values of 2 items in the queue
function comparator (a, b) {
return a < b ? true : false
}
// create a new priority queue that can hold a maximum of 20,000 items.
// by default max length is 1000
const MAX_LENGTH = 20000
const obj = PQ.create(comparator, MAX_LENGTH)
// insert a few items
PQ.queue(obj, 'e', 1)
PQ.queue(obj, 'f', 9)
PQ.queue(obj, 'g', 4)
// get the highest priority item out of the queue
console.log(PQ.dequeue(obj)) // 'f'
console.log(PQ.dequeue(obj)) // 'g'
console.log(PQ.dequeue(obj)) // 'e'
// when the queue is empty it'll return undefined on dequeue
console.log(PQ.dequeue(obj)) // undefined
By default dequeue will return the highest prioritied item in the queue first. If you want to get the lowest priority item instead, pass a 3rd boolean argument:
const highest = PQ.dequeue(obj)
GET_HIGHEST = false
const lowest = PQ.dequeue(obj, GET_HIGHEST)
API
queue
- add an element to the queuedequeue
- delete the max priority element from the queueisEmpty
- returns true/falseclear
- clear the queuedelete
- If we need to update the priority, delete that item and insert it in againlist
- contents of heap
The Item stored in the queue should be class and a comparator should be provided.
If values in a queue are strings, comparator will receive priorities as a and b in the example below
We need max priority element to be removed first.
const comparator = function (a, b) {
return a >= b ? false : true
}
An example would be:
const obj = PriorityQueue.create(comparator)
PQ.queue(obj, 'c', 1)
PQ.queue(obj, 'b', 3)
PQ.queue(obj, 'a', 5)
console.log(PQ.dequeue(obj)) //'a'
If values in the queue is an object, comparator will receive the object and you need to compare priorities
class Box {
constructor(w, l) {
this.w = w
this.l = l
this.area = w * l //this is priority
}
comparator(a, b) {
return a.area >= b.area ? false : true
}
}
const obj = PQ.create(Box.prototype.comparator)
const a = new Box(5, 5)
const b = new Box(9, 9)
PQ.queue(obj, a)
PQ.queue(obj, new Box(2, 3))
PQ.queue(obj, new Box(3, 3))
PQ.queue(obj, b)
assert.deepEqual(PQ.dequeue(obj), b)
assert.deepEqual(PQ.dequeue(obj), a)