dijsktra.java

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[], int n) 
    { 
        System.out.println("Vertex   Distance from Source"); 
        for (int i = 0; i < V; i++) 
            System.out.println(i+" tt "+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) 
    { 
        /* 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); 
    } 
}