Matrix reading from file Dijkstra's Algorithm

Question

I have a shortest path algorithm in place and have fully understood its working, but instead of taking the matrix input inside the main function the code I want to read the matrix from a text file. I am a beginer and just trying to learn how this code works. I dont claim any ownership to the code give below.

here is the entire code I'm using.

// A Java program for Dijkstra's single source shortest path algorithm.
// The program is for adjacency matrix representation of the graph
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=5;
    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[], int n)
    {
        System.out.println("Distance from starting vertex");
        for (int i = 0; i < V; i++)
            System.out.println(i+" \t\t "+dist[i]);
    }

    // Funtion 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, V);
    }

    // Driver method
    public static void main (String[] args)
    {
       int graph[][] = new int[][] {{0, 14, 0, 0, 0},
                                   {0, 0, 3, 10, 0},
                                   {0, 0, 0, 4,  0},
                                   {0, 0, 0, 0, 10},
                                   {0, 0, 0, 0,  0},
                                 };
        ShortestPath t = new ShortestPath();
        t.dijkstra(graph, 0);
    }
}

I have a matrix in the text file but how do i make the program read it in — Vikram AJ, Oct 06 '16 at 17:52
I came up with simple code input = new Scanner(new File("src/array.txt")); for(int i = 0; i < rows; ++i) { for(int j = 0; j < columns; ++j) { if(input.hasNextInt()) { a[i][j] = input.nextInt(); } } } — Vikram AJ, Oct 06 '16 at 17:53
http://stackoverflow.com/questions/4769976/reading-2-d-array-from-a-file — NiVeR, Oct 06 '16 at 17:55
I think the problem here is just how to read data from file? I don't see how Dijkstra's algo related here? — Pham Trung, Oct 06 '16 at 18:21

score 0 · Answer 1 · answered Oct 08 '16 at 14:09

 File file = new File("10_Random.txt");
    try {

        Scanner sc = new Scanner(file);
        int graph[][] = new int[5][5];
        for(int i = 0 ; i < 5; i++){
            for(int j = 0 ; j < 5; j++){
                graph[i][j] = sc.nextInt();
            }
        }
        sc.close();
    }
    catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

put that inside the main function.

Matrix reading from file Dijkstra's Algorithm

1 Answers1