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DijkstrasAlgo.java
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DijkstrasAlgo.java
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import java.util.*;
public class DijkstrasAlgo {
public static void main(String args[]) {
int V = 6;
ArrayList<Edge> graph[] = new ArrayList[V];
createGraph(graph);
int src = 0;
dijkstra(graph, src);
}
static class Edge {
int src, dest, wt;
public Edge(int s, int d, int w) {
this.src = s;
this.dest = d;
this.wt = w;
}
}
public static void createGraph(ArrayList<Edge> graph[]) {
for(int i=0; i<graph.length; i++) {
graph[i] = new ArrayList<>();
}
graph[0].add(new Edge(0, 1, 2));
graph[0].add(new Edge(0, 2, 4));
graph[1].add(new Edge(1, 3, 7));
graph[1].add(new Edge(1, 2, 1));
graph[2].add(new Edge(2, 4, 3));
graph[3].add(new Edge(3, 5, 1));
graph[4].add(new Edge(4, 3, 2));
graph[4].add(new Edge(4, 5, 5));
}
public static void dijkstra(ArrayList<Edge> graph[], int src) {
int dist[] = new int[graph.length]; //dist[i] --> src to i
for (int i=0; i<graph.length; i++) {
if (i!=src) {
dist[i] = Integer.MAX_VALUE; //Initialise with infinity
}
}
PriorityQueue<Pair> pq = new PriorityQueue<>();
pq.add(new Pair(src, 0)); //Initially src with path value == 0;
boolean vis[] = new boolean[graph.length];
while(!pq.isEmpty()) {
Pair curr = pq.remove();
if(!vis[curr.n]) {
vis[curr.n] = true;
//Now call for all the neighbours of teh curr.n(currNode)
for(int i=0; i<graph[curr.n].size(); i++) {
Edge e = graph[curr.n].get(i);
int u = e.src;
int v = e.dest;
int w = e.wt;
//initially dist[v] is infinity :-
//Hence every path will be added to pq as a pair(node, path);
if (dist[u]+w < dist[v]) {
dist[v] = dist[u]+w;
pq.add(new Pair(v, dist[v]));
//adding v as new node;
//adding dist[v] as new path;
}
}
}
}
for (int i=0; i<dist.length; i++) {
System.out.print(dist[i] + " ");
}
System.out.println();
}
static class Pair implements Comparable<Pair> {
int n, path;
// n --> Node
// path --> Path from src -> dest;
public Pair(int n, int path){
this.n = n;
this.path = path;
}
@Override
public int compareTo(Pair p2) {
return this.path - p2.path; //Path based sorting for pairs
}
}
}