README.md

@datastructures-js/priority-queue

A performant priority queue implementation using a Heap data structure.

Table of Contents

• Install
• API
  • require
  • import
  • Construction
  • .enqueue(element[, priority])
  • .front()
  • .back()
  • .dequeue()
  • .isEmpty()
  • .size()
  • .toArray()
  • .clear()
• Build
• License

Install

npm install --save @datastructures-js/priority-queue

API

There are two types of PriorityQueue in this repo: MinPriorityQueue which uses a MinHeap and considers an element with smaller priority number as higher in priority. And MaxPriorityQueue which uses a MaxHeap and cosiders an element with bigger priority number as higher in priority.

require

const { MinPriorityQueue, MaxPriorityQueue } = require('@datastructures-js/priority-queue');

import

import { MinPriorityQueue, MaxPriorityQueue } from '@datastructures-js/priority-queue';

Construction

The constructor can accept a callback to get the priority from the queued element. If not passed, the priortiy should be passed with .enqueue.

Example

// the priority not part of the enqueued element
const patientsQueue = new MinPriorityQueue();

// the priority is a prop of the queued element
const biddersQueue = new MaxPriorityQueue({ priority: (bid) => bid.value });

.enqueue(element[, priority])

adds an element with a priority (number) to the queue. Priority is not required here if a priority callback has been defined in the constructor. If passed here in addition to an existing constructor callback, it will override the callback one.

params
name	type
element	object
priority	number

runtime
O(log(n))

Example

// MinPriorityQueue Example, where priority is the turn for example
patientsQueue.enqueue('patient y', 1); // highest priority
patientsQueue.enqueue('patient z', 3);
patientsQueue.enqueue('patient w', 4); // lowest priority
patientsQueue.enqueue('patient x', 2);

// MaxPriorityQueue Example, where priority is the bid for example. Priority is obtained from the callback.
biddersQueue.enqueue({ name: 'bidder y', value: 1000 }); // lowest priority
biddersQueue.enqueue({ name: 'bidder w', value: 2500 });
biddersQueue.enqueue({ name: 'bidder z', value: 3500 }); // highest priority
biddersQueue.enqueue({ name: 'bidder x', value: 3000 });

.front()

returns the element with highest priority in the queue.

return	description
object	object literal with "priority" and "element" props

runtime
O(1)

Example

console.log(patientsQueue.front()); // { priority: 1, element: 'patient y' }

console.log(biddersQueue.front()); // { priority: 3500, element: { name: 'bidder z', value: 3500 } }

.back()

returns an element with lowest priority in the queue. If multiple elements exist at the lowest priority, the one that was inserted first will be returned.

return	description
object	object literal with "priority" and "element" props

runtime
O(1)

Example

patientsQueue.enqueue('patient m', 4); // lowest priority
patientsQueue.enqueue('patient c', 4); // lowest priority
console.log(patientsQueue.back()); // { priority: 4, element: 'patient w' }

biddersQueue.enqueue({ name: 'bidder m', value: 1000 }); // lowest priority
biddersQueue.enqueue({ name: 'bidder c', value: 1000 }); // lowest priority
console.log(biddersQueue.back()); // { priority: 1000, element: { name: 'bidder y', value: 1000 } }

.dequeue()

removes and returns the element with highest priority in the queue.

return	description
object	object literal with "priority" and "element" props

runtime
O(log(n))

Example

console.log(patientsQueue.dequeue()); // { priority: 1, element: 'patient y' }
console.log(patientsQueue.front()); // { priority: 2, element: 'patient x' }

console.log(biddersQueue.dequeue()); // { priority: 3500, element: { name: 'bidder z', value: 3500 } }
console.log(biddersQueue.front()); // { priority: 3000, element: { name: 'bidder x', value: 3000 } }

.isEmpty()

checks if the queue is empty.

return
boolean

runtime
O(1)

Example

console.log(patientsQueue.isEmpty()); // false

console.log(biddersQueue.isEmpty()); // false

.size()

returns the number of elements in the queue.

return
number

runtime
O(1)

Example

console.log(patientsQueue.size()); // 5

console.log(biddersQueue.size()); // 5

.toArray()

returns a sorted array of elements by their priorities from highest to lowest.

return	description
array	an array of object literals with "priority" & "element" props

runtime
O(n*log(n))

Example

console.log(patientsQueue.toArray());
/*
[
  { priority: 2, element: 'patient x' },
  { priority: 3, element: 'patient z' },
  { priority: 4, element: 'patient c' },
  { priority: 4, element: 'patient w' },
  { priority: 4, element: 'patient m' }
]
*/

console.log(biddersQueue.toArray());
/*
[
  { priority: 3000, element: { name: 'bidder x', value: 3000 } },
  { priority: 2500, element: { name: 'bidder w', value: 2500 } },
  { priority: 1000, element: { name: 'bidder y', value: 1000 } },
  { priority: 1000, element: { name: 'bidder m', value: 1000 } },
  { priority: 1000, element: { name: 'bidder c', value: 1000 } }
]
*/

.clear()

clears all elements in the queue.

runtime
O(1)

Example

patientsQueue.clear();
console.log(patientsQueue.size()); // 0
console.log(patientsQueue.front()); // null
console.log(patientsQueue.dequeue()); // null

biddersQueue.clear();
console.log(biddersQueue.size()); // 0
console.log(biddersQueue.front()); // null
console.log(biddersQueue.dequeue()); // null

Build

grunt build

License

The MIT License. Full License is here