Dijkstra Algorithm Java

PROGRAM TO IMPLEMENT DIJKSTRA'S ALGORITHM




import java.util.*;

import java.lang.*;

import java.io.*;

  

class ShortestPath {

    // A utility function to find the vertex with minimum distance value,

    // from the set of vertices not yet included in shortest path tree

    static final int V = 9;

    int minDistance(int dist[], Boolean sptSet[])

    {

        // Initialize min value

        int min = Integer.MAX_VALUE, min_index = -1;

  

        for (int v = 0; v < V; v++)

            if (sptSet[v] == false && dist[v] <= min) {

                min = dist[v];

                min_index = v;

            }

  

        return min_index;

    }

  

    // A utility function to print the constructed distance array

    void printSolution(int dist[])

    {

        System.out.println("Vertex \t\t Distance from Source");

        for (int i = 0; i < V; i++)

            System.out.println(i + " \t\t " + dist[i]);

    }

  

    // Function that implements Dijkstra's single source shortest path

    // algorithm for a graph represented using adjacency matrix

    // representation

    void dijkstra(int graph[][], int src)

    {

        int dist[] = new int[V]; // The output array. dist[i] will hold

        // the shortest distance from src to i

  

        // sptSet[i] will true if vertex i is included in shortest

        // path tree or shortest distance from src to i is finalized

        Boolean sptSet[] = new Boolean[V];

  

        // Initialize all distances as INFINITE and stpSet[] as false

        for (int i = 0; i < V; i++) {

            dist[i] = Integer.MAX_VALUE;

            sptSet[i] = false;

        }

  

        // Distance of source vertex from itself is always 0

        dist[src] = 0;

  

        // Find shortest path for all vertices

        for (int count = 0; count < V - 1; count++) {

            // Pick the minimum distance vertex from the set of vertices

            // not yet processed. u is always equal to src in first

            // iteration.

            int u = minDistance(dist, sptSet);

  

            // Mark the picked vertex as processed

            sptSet[u] = true;

  

            // Update dist value of the adjacent vertices of the

            // picked vertex.

            for (int v = 0; v < V; v++)

  

                // Update dist[v] only if is not in sptSet, there is an

                // edge from u to v, and total weight of path from src to

                // v through u is smaller than current value of dist[v]

                if (!sptSet[v] && graph[u][v] != 0 && dist[u] != Integer.MAX_VALUE && dist[u] + graph[u][v] < dist[v])

                    dist[v] = dist[u] + graph[u][v];

        }

  

        // print the constructed distance array

        printSolution(dist);

    }

  

    // Driver method

    public static void main(String[] args)

    {

        /* Let us create the example graph discussed above */

        int graph[][] = new int[][] { { 0, 4, 0, 0, 0, 0, 0, 8, 0 },

                                      { 4, 0, 8, 0, 0, 0, 0, 11, 0 },

                                      { 0, 8, 0, 7, 0, 4, 0, 0, 2 },

                                      { 0, 0, 7, 0, 9, 14, 0, 0, 0 },

                                      { 0, 0, 0, 9, 0, 10, 0, 0, 0 },

                                      { 0, 0, 4, 14, 10, 0, 2, 0, 0 },

                                      { 0, 0, 0, 0, 0, 2, 0, 1, 6 },

                                      { 8, 11, 0, 0, 0, 0, 1, 0, 7 },

                                      { 0, 0, 2, 0, 0, 0, 6, 7, 0 } };

        ShortestPath t = new ShortestPath();

        t.dijkstra(graph, 0);

    }

}




OUTPUT:

Vertex   Distance from Source
0                0
1                4
2                12
3                19
4                21
5                11
6                9
7                8
8                14

CREDITS: https://www.geeksforgeeks.org/dijkstras-shortest-path-algorithm-greedy-algo-7/