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| class WeightedGraph {
constructor() {
this.adjacencyList = {};
}
addVertex(vertex){
if(!this.adjacencyList[vertex]) this.adjacencyList[vertex] = [];
}
addEdge(vertex1,vertex2, weight){
this.adjacencyList[vertex1].push({node:vertex2,weight});
this.adjacencyList[vertex2].push({node:vertex1, weight});
}
Dijkstra(start, finish){
const nodes = new PriorityQueue();
const distances = {};
const previous = {};
let path = [] //to return at end
let smallest;
//build up initial state
for(let vertex in this.adjacencyList){
if(vertex === start){
distances[vertex] = 0;
nodes.enqueue(vertex, 0);
} else {
distances[vertex] = Infinity;
nodes.enqueue(vertex, Infinity);
}
previous[vertex] = null;
}
// as long as there is something to visit
while(nodes.values.length){
smallest = nodes.dequeue().val;
if(smallest === finish){
//WE ARE DONE
//BUILD UP PATH TO RETURN AT END
while(previous[smallest]){
path.push(smallest);
smallest = previous[smallest];
}
break;
}
if(smallest || distances[smallest] !== Infinity){
for(let neighbor in this.adjacencyList[smallest]){
//find neighboring node
let nextNode = this.adjacencyList[smallest][neighbor];
//calculate new distance to neighboring node
let candidate = distances[smallest] + nextNode.weight;
let nextNeighbor = nextNode.node;
if(candidate < distances[nextNeighbor]){
//updating new smallest distance to neighbor
distances[nextNeighbor] = candidate;
//updating previous - How we got to neighbor
previous[nextNeighbor] = smallest;
//enqueue in priority queue with new priority
nodes.enqueue(nextNeighbor, candidate);
}
}
}
}
return path.concat(smallest).reverse();
}
}
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 min = this.values[0];
const end = this.values.pop();
if(this.values.length > 0){
this.values[0] = end;
this.sinkDown();
}
return min;
}
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(val, priority){
this.val = val;
this.priority = priority;
}
}
var graph = new WeightedGraph()
graph.addVertex("A");
graph.addVertex("B");
graph.addVertex("C");
graph.addVertex("D");
graph.addVertex("E");
graph.addVertex("F");
graph.addEdge("A","B", 4);
graph.addEdge("A","C", 2);
graph.addEdge("B","E", 3);
graph.addEdge("C","D", 2);
graph.addEdge("C","F", 4);
graph.addEdge("D","E", 3);
graph.addEdge("D","F", 1);
graph.addEdge("E","F", 1);
graph.Dijkstra("A", "E");
|