Dijkastras Algorithm using Priority Queue

Impossible Ibis answered on February 1, 2023 Popularity 9/10 Helpfulness 1/10

answer Dijkastras Algorithm using Priority Queue

Dijkastras Algorithm using Priority Queue

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// Java Program to Implement Dijkstra's Algorithm
// Using Priority Queue
 
// Importing utility classes
import java.util.*;
 
// Main class DPQ
public class GFG {
 
    // Member variables of this class
    private int dist[];
    private Set<Integer> settled;
    private PriorityQueue<Node> pq;
    // Number of vertices
    private int V;
    List<List<Node> > adj;
 
    // Constructor of this class
    public GFG(int V)
    {
 
        // This keyword refers to current object itself
        this.V = V;
        dist = new int[V];
        settled = new HashSet<Integer>();
        pq = new PriorityQueue<Node>(V, new Node());
    }
 
    // Method 1
    // Dijkstra's Algorithm
    public void dijkstra(List<List<Node> > adj, int src)
    {
        this.adj = adj;
 
        for (int i = 0; i < V; i++)
            dist[i] = Integer.MAX_VALUE;
 
        // Add source node to the priority queue
        pq.add(new Node(src, 0));
 
        // Distance to the source is 0
        dist[src] = 0;
 
        while (settled.size() != V) {
 
            // Terminating condition check when
            // the priority queue is empty, return
            if (pq.isEmpty())
                return;
 
            // Removing the minimum distance node
            // from the priority queue
            int u = pq.remove().node;
 
            // Adding the node whose distance is
            // finalized
            if (settled.contains(u))
 
                // Continue keyword skips execution for
                // following check
                continue;
 
            // We don't have to call e_Neighbors(u)
            // if u is already present in the settled set.
            settled.add(u);
 
            e_Neighbours(u);
        }
    }
 
    // Method 2
    // To process all the neighbours
    // of the passed node
    private void e_Neighbours(int u)
    {
 
        int edgeDistance = -1;
        int newDistance = -1;
 
        // All the neighbors of v
        for (int i = 0; i < adj.get(u).size(); i++) {
            Node v = adj.get(u).get(i);
 
            // If current node hasn't already been processed
            if (!settled.contains(v.node)) {
                edgeDistance = v.cost;
                newDistance = dist[u] + edgeDistance;
 
                // If new distance is cheaper in cost
                if (newDistance < dist[v.node])
                    dist[v.node] = newDistance;
 
                // Add the current node to the queue
                pq.add(new Node(v.node, dist[v.node]));
            }
        }
    }
 
    // Main driver method
    public static void main(String arg[])
    {
 
        int V = 5;
        int source = 0;
 
        // Adjacency list representation of the
        // connected edges by declaring List class object
        // Declaring object of type List<Node>
        List<List<Node> > adj
            = new ArrayList<List<Node> >();
 
        // Initialize list for every node
        for (int i = 0; i < V; i++) {
            List<Node> item = new ArrayList<Node>();
            adj.add(item);
        }
 
        // Inputs for the GFG(dpq) graph
        adj.get(0).add(new Node(1, 9));
        adj.get(0).add(new Node(2, 6));
        adj.get(0).add(new Node(3, 5));
        adj.get(0).add(new Node(4, 3));
 
        adj.get(2).add(new Node(1, 2));
        adj.get(2).add(new Node(3, 4));
 
        // Calculating the single source shortest path
        GFG dpq = new GFG(V);
        dpq.dijkstra(adj, source);
 
        // Printing the shortest path to all the nodes
        // from the source node
        System.out.println("The shorted path from node :");
 
        for (int i = 0; i < dpq.dist.length; i++)
            System.out.println(source + " to " + i + " is "
                               + dpq.dist[i]);
    }
}
 
// Class 2
// Helper class implementing Comparator interface
// Representing a node in the graph
class Node implements Comparator<Node> {
 
    // Member variables of this class
    public int node;
    public int cost;
 
    // Constructors of this class
 
    // Constructor 1
    public Node() {}
 
    // Constructor 2
    public Node(int node, int cost)
    {
 
        // This keyword refers to current instance itself
        this.node = node;
        this.cost = cost;
    }
 
    // Method 1
    @Override public int compare(Node node1, Node node2)
    {
 
        if (node1.cost < node2.cost)
            return -1;
 
        if (node1.cost > node2.cost)
            return 1;
 
        return 0;
    }
}

Popularity 9/10 Helpfulness 1/10 Language whatever

Source: www.geeksforgeeks.org

Tags: algorithm priority-queue using whatever

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Contributed on Feb 01 2023

Impossible Ibis

0 Answers Avg Quality 2/10

Dijkastras Algorithm using Priority Queue

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