datastructures-js@datastructures-js/queue
A performant queue implementation in javascript.
Contents
Install
npm install --save @datastructures-js/queue
require
const { Queue } = require('@datastructures-js/queue');
import
import { Queue } from '@datastructures-js/queue';
API
constructor
JS
// empty queue
const queue = new Queue();
// from an array
const queue = new Queue([1, 2, 3]);
TS
// empty queue
const queue = new Queue<number>();
// from an array
const queue = new Queue<number>([1, 2, 3]);
Queue.fromArray
JS
// empty queue
const queue = Queue.fromArray([]);
// with elements
const list = [10, 3, 8, 40, 1];
const queue = Queue.fromArray(list);
// If the list should not be mutated, use a copy of it.
const queue = Queue.fromArray(list.slice());
TS
// empty queue
const queue = Queue.fromArray<number>([]);
// with elements
const list = [10, 3, 8, 40, 1];
const queue = Queue.fromArray<number>(list);
enqueue (push)
adds an element to the back of the queue.
queue.enqueue(10).enqueue(20); // or queue.push(123)
front
peeks on the front element of the queue.
console.log(queue.front()); // 10
back
peeks on the back element in the queue.
console.log(queue.back()); // 20
dequeue (pop)
removes and returns the front element of the queue in O(1) runtime.
console.log(queue.dequeue()); // 10 // or queue.pop()
console.log(queue.front()); // 20
Dequeuing all elements takes O(n) instead of O(n2) when using shift/unshift with arrays.
Explanation by @alexypdu:
Internally, when half the elements have been dequeued, we will resize the dynamic array using Array.slice() which runs in $O(n)$. Since dequeuing all $n$ elements will resize the array $\log_2n$ times, the complexity is $$1 + 2 + 4 + \cdots + 2^{\log_2 n - 1} = 2 ^ {(\log_2 n - 1) + 1} - 1 = n - 1 = O(n)$$ Hence the overall complexity of dequeuing all elements is $O(n + n) = O(n)$, and the amortized complexity of dequeue() is thus $O(1)$.
benchmark:
dequeuing 1 million elements in Node v14
| Queue.dequeue | Array.shift |
| ~27 ms | ~4 mins 31 secs |
isEmpty
checks if the queue is empty.
console.log(queue.isEmpty()); // false
size
returns the number of elements in the queue.
console.log(queue.size()); // 1
clone
creates a shallow copy of the queue.
const queue = Queue.fromArray([{ id: 2 }, { id: 4 } , { id: 8 }]);
const clone = queue.clone();
clone.dequeue();
console.log(queue.front()); // { id: 2 }
console.log(clone.front()); // { id: 4 }
toArray
returns a copy of the remaining elements as an array.
queue.enqueue(4).enqueue(2);
console.log(queue.toArray()); // [20, 4, 2]
clear
clears all elements from the queue.
queue.clear();
queue.size(); // 0
Build
grunt build
License
The MIT License. Full License is here