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// Priority Queue Helper functions
functiongetParentPosition(position){
// Get the parent node of the current node
returnMath.floor((position-1)/2)
}
functiongetChildrenPosition(position){
// Get the children nodes of the current node
return[2*position+1,2*position+2]
}
classPriorityQueue{
// Priority Queue class using Minimum Binary Heap
constructor(){
this._heap=[]
this.keys={}
}
isEmpty(){
// Checking if the heap is empty
returnthis._heap.length===0
}
push(key,priority){
// Adding element to the queue (equivalent to add)
this._heap.push([key,priority])
this.keys[key]=this._heap.length-1
this._shiftUp(this.keys[key])
}
pop(){
// Removing the element with least priority (equivalent to extractMin)
this._swap(0,this._heap.length-1)
const[key]=this._heap.pop()
deletethis.keys[key]
this._shiftDown(0)
returnkey
}
contains(key){
// Check if a given key is present in the queue
return(keyinthis.keys)
}
update(key,priority){
// Update the priority of the given element (equivalent to decreaseKey)
constcurrPos=this.keys[key]
this._heap[currPos][1]=priority
constparentPos=getParentPosition(currPos)
constcurrPriority=this._heap[currPos][1]
letparentPriority=Infinity
if(parentPos>=0){
parentPriority=this._heap[parentPos][1]
}
const[child1Pos,child2Pos]=getChildrenPosition(currPos)
let[child1Priority,child2Priority]=[Infinity,Infinity]
if(child1Pos<this._heap.length){
child1Priority=this._heap[child1Pos][1]
}
if(child2Pos<this._heap.length){
child2Priority=this._heap[child2Pos][1]
}
if(parentPos>=0&&parentPriority>currPriority){
this._shiftUp(currPos)
}elseif(child2Pos<this._heap.length&&
(child1Priority<currPriority||child2Priority<currPriority)){
this._shiftDown(currPos)
}
}
_shiftUp(position){
// Helper function to shift up a node to proper position (equivalent to bubbleUp)
letcurrPos=position
letparentPos=getParentPosition(currPos)
letcurrPriority=this._heap[currPos][1]
letparentPriority=Infinity
if(parentPos>=0){
parentPriority=this._heap[parentPos][1]
}
while(parentPos>=0&&parentPriority>currPriority){
this._swap(currPos,parentPos)
currPos=parentPos
parentPos=getParentPosition(currPos)
currPriority=this._heap[currPos][1]
try{
parentPriority=this._heap[parentPos][1]
}catch(error){
parentPriority=Infinity
}
}
this.keys[this._heap[currPos][0]]=currPos
}
_shiftDown(position){
// Helper function to shift down a node to proper position (equivalent to bubbleDown)
letcurrPos=position
let[child1Pos,child2Pos]=getChildrenPosition(currPos)
let[child1Priority,child2Priority]=[Infinity,Infinity]
if(child1Pos<this._heap.length){
child1Priority=this._heap[child1Pos][1]
}
if(child2Pos<this._heap.length){
child2Priority=this._heap[child2Pos][1]
}
letcurrPriority
try{
currPriority=this._heap[currPos][1]
}catch{
return
}
while(child2Pos<this._heap.length&&
(child1Priority<currPriority||child2Priority<currPriority)){
if(child1Priority<currPriority&&child1Priority<child2Priority){
this._swap(child1Pos,currPos)
currPos=child1Pos
}else{
this._swap(child2Pos,currPos)
currPos=child2Pos
}
[child1Pos,child2Pos]=getChildrenPosition(currPos)
try{
[child1Priority,child2Priority]=[this._heap[child1Pos][1],this._heap[child2Pos][1]]
}catch(error){
[child1Priority,child2Priority]=[Infinity,Infinity]
}
currPriority=this._heap[currPos][1]
}
this.keys[this._heap[currPos][0]]=currPos
if(child1Pos<this._heap.length&&child1Priority<currPriority){
this._swap(child1Pos,currPos)
this.keys[this._heap[child1Pos][0]]=child1Pos
}
}
_swap(position1,position2){
// Helper function to swap 2 nodes
[this._heap[position1],this._heap[position2]]=[this._heap[position2],this._heap[position1]]
this.keys[this._heap[position1][0]]=position1
this.keys[this._heap[position2][0]]=position2
}
}
classGraphWeightedUndirectedAdjacencyList{
// Weighted Undirected Graph class
constructor(){
this.connections={}
}
addNode(node){
// Function to add a node to the graph (connection represented by set)
this.connections[node]={}
}
addEdge(node1,node2,weight){
// Function to add an edge (adds the node too if they are not present in the graph)
if(!(node1inthis.connections)){this.addNode(node1)}
if(!(node2inthis.connections)){this.addNode(node2)}
this.connections[node1][node2]=weight
this.connections[node2][node1]=weight
}
PrimMST(start){
// Prim's Algorithm to generate a Minimum Spanning Tree (MST) of a graph
// Details: https://en.wikipedia.org/wiki/Prim%27s_algorithm
constdistance={}
constparent={}
constpriorityQueue=newPriorityQueue()
// Initialization
for(constnodeinthis.connections){
distance[node]=(node===start.toString() ? 0 : Infinity)
parent[node]=null
priorityQueue.push(node,distance[node])
}
// Updating 'distance' object
while(!priorityQueue.isEmpty()){
constnode=priorityQueue.pop()
Object.keys(this.connections[node]).forEach(neighbour=>{
if(priorityQueue.contains(neighbour)&&distance[node]+this.connections[node][neighbour]<distance[neighbour]){
distance[neighbour]=distance[node]+this.connections[node][neighbour]
parent[neighbour]=node
priorityQueue.update(neighbour,distance[neighbour])
}
})
}
// MST Generation from the 'parent' object
constgraph=newGraphWeightedUndirectedAdjacencyList()
Object.keys(parent).forEach(node=>{
if(node&&parent[node]){
graph.addEdge(node,parent[node],this.connections[node][parent[node]])
}
})
returngraph
}
}
export{GraphWeightedUndirectedAdjacencyList}
// const graph = new GraphWeightedUndirectedAdjacencyList()
// graph.addEdge(1, 2, 1)
// graph.addEdge(2, 3, 2)
// graph.addEdge(3, 4, 1)
// graph.addEdge(3, 5, 100) // Removed in MST
// graph.addEdge(4, 5, 5)
// graph.PrimMST(1)