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priority_queue.js
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priority_queue.js
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/*Priority Queue - a Data Structure where each element has a priority.
Elements with higher priorities are served before elements with lower priority
*/
class PriorityQueue {
constructor() {
this.values = []
}
enqueue(val, priority) {
let newNode = new Node(val, priority)
this.values.push(newNode)
this.bubbleUp()
}
bubbleUp() {
let idx = this.values.length - 1
const element = this.values[idx]
while(idx > 0) {
let parentIdx = Math.floor((idx - 1)/2)
let parent = this.values[parentIdx]
if(element.priority <= parent.priority) break
this.values[parentIdx] = element
this.values[idx] = parent
idx = parentIdx
}
}
dequeue() {
const max = this.values[0]
const end = this.values.pop()
if(this.values.length > 0) {
this.values[0] = end
this.sinkDown()
}
return max
}
sinkDown() {
let idx = 0
const length = this.values.length
const element = this.values[0]
while(true) {
let leftChildIdx = 2 * idx + 1
let rightChildIdx = 2 * idx + 2
let leftChild, rightChild
let swap = null
if(leftChildIdx < length) {
leftChild = this.values[leftChildIdx]
if(leftChild.priority > element.priority) {
swap = leftChildIdx
}
}
if(rightChildIdx < length) {
rightChild = this.values[rightChildIdx]
if(
(swap === null && rightChild.priority > element.priority) ||
(swap !== null && rightChild.priority > leftChild.priority)
) {
swap = rightChildIdx
}
}
if(swap === null) break
this.values[idx] = this.values[swap]
this.values[swap] = element
idx = swap
}
}
}
class Node {
constructor(value, priority) {
this.val = this.val
this.priority = priority
}
}
let ER = new PriorityQueue()
console.log(ER.enqueue("Common Cold", 1))
console.log(ER.enqueue("Gun Shot Wound", 5))
console.log(ER.enqueue("High Fever", 2))