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Simple Javascript Heap implementation
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// usage: | |
// create a min heap | |
// const heap = new Heap((a, b) => a.val < b.val) | |
// | |
// create a max heap | |
// const heap = new Heap((a, b) => a.val > b.val) | |
// | |
// insert an item into the heap - O(lgn) | |
// heap.insert(item) | |
// | |
// check if the heap is empty - O(1) | |
// if (heap.isEmpty()) {... | |
// | |
// delete and retrieve the root element of the heap - O(lgn) | |
// let next = heap.delete() | |
class Heap { | |
#items | |
#comparator | |
constructor(comparator) { | |
this.#items = [] | |
this.#comparator = comparator | |
} | |
count() { | |
return this.#items.length | |
} | |
isEmpty() { | |
return this.#items.length == 0 | |
} | |
delete() { | |
if (this.isEmpty()) { | |
return null | |
} | |
const val = this.#items[0] | |
this.#items[0] = this.#items[this.#items.length - 1] | |
this.#items.pop() | |
if (!this.isEmpty()) { | |
this.#heapify(0) | |
} | |
return val | |
} | |
insert(value) { | |
this.#items.push(value) | |
this.#reverseHeapify(this.#items.length - 1) | |
} | |
#parent(index) { | |
const p = (index - 1) / 2 | |
return Math.floor(p) | |
} | |
#left(index) { | |
return index * 2 + 1 | |
} | |
#right(index) { | |
return index * 2 + 2 | |
} | |
#reverseHeapify(index) { | |
if (index <= 0) { | |
return | |
} | |
const p = this.#parent(index) | |
if (this.#comparator(this.#items[index], this.#items[p])) { | |
this.#swap(p, index) | |
this.#reverseHeapify(p) | |
} | |
} | |
#swap(i, j) { | |
const tmp = this.#items[i] | |
this.#items[i] = this.#items[j] | |
this.#items[j] = tmp | |
} | |
#heapify(index) { | |
const l = this.#left(index) | |
const r = this.#right(index) | |
let smallest = index | |
if (l < this.#items.length && this.#comparator(this.#items[l], this.#items[index])) { | |
smallest = l | |
} | |
if (r < this.#items.length && this.#comparator(this.#items[r], this.#items[smallest])) { | |
smallest = r | |
} | |
if (smallest != index) { | |
this.#swap(smallest, index) | |
this.#heapify(smallest) | |
} | |
} | |
} |
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you need to use comparator
(a, b) => a < b
or insert items where they have the number stored in a val property