Dijkstra.java

Dijkstra.java

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+// A Java program that finds the shortest path using Dijkstra's algorithm.  
+// The program uses the adjacency matrix for the representation of a graph   
+
+// import statements  
+import java.util.*;  
+import java.io.*;  
+import java.lang.*;  
+
+public class DijkstraExample   
+{  
+// A utility method to compute the vertex with the distance value, which is minimum  
+// from the group of vertices that has not been included yet   
+static final int totalVertex = 9;  
+int minimumDistance(int distance[], Boolean spSet[])  
+{  
+// Initialize min value  
+int m = Integer.MAX_VALUE, m_index = -1;  
+
+for (int vx = 0; vx < totalVertex; vx++)  
+{  
+if (spSet[vx] == false && distance[vx] <= m)   
+{  
+m = distance[vx];  
+m_index = vx;  
+}  
+}  
+return m_index;  
+
+}  
+
+// A utility method to display the built distance array  
+void printSolution(int distance[], int n)  
+{  
+System.out.println("The shortest Distance from source 0th node to all other nodes are: ");  
+for (int j = 0; j < n; j++)  
+System.out.println("To " + j + " the shortest distance is: " + distance[j]);  
+}  
+
+// method that does the implementation of Dijkstra's shortest path algorithm  
+// for a graph that is being represented using the adjacency matrix representation  
+void dijkstra(int graph[][], int s)  
+{  
+int distance[] = new int[totalVertex]; // The output array distance[i] holds the shortest distance from source s to j  
+
+// spSet[j] will be true if vertex j is included in the shortest  
+// path tree or the shortest distance from the source s to j is finalized  
+Boolean spSet[] = new Boolean[totalVertex];  
+
+// Initializing all of the distances as INFINITE   
+// and spSet[] as false  
+for (int j = 0; j < totalVertex; j++)   
+{  
+distance[j] = Integer.MAX_VALUE;  
+spSet[j] = false;  
+}  
+
+// Distance from the source vertex to itself is always 0  
+distance[s] = 0;  
+
+// compute the shortest path for all the given vertices  
+for (int cnt = 0; cnt < totalVertex - 1; cnt++)   
+{  
+// choose the minimum distance vertex from the set of vertices  
+// not yet processed. ux is always equal to source s in the first  
+// iteration.  
+int ux = minimumDistance(distance, spSet);  
+
+// the choosed vertex is marked as true  
+// it means it is processed  
+spSet[ux] = true;  
+
+// Updating the distance value of the neighboring vertices   
+// of the choosed vertex.  
+for (int vx = 0; vx < totalVertex; vx++)  
+
+// Update distance[vx] if and only if it is not in the spSet, there is an  
+// edge from ux to vx, and the total weight of path from source s to  
+// vx through ux is lesser than the current value of distance[vx]  
+if (!spSet[vx] && graph[ux][vx] != -1 && distance[ux] != Integer.MAX_VALUE && distance[ux] + graph[ux][vx] < distance[vx])  
+{  
+distance[vx] = distance[ux] + graph[ux][vx];  
+}  
+}  
+
+// display the build distance array  
+printSolution(distance, totalVertex);  
+}  
+
+// main method  
+public static void main(String argvs[])  
+{  
+// A 9 * 9 matrix is created.   
+// arr[x][y] = - 1 means, there is no any edge that connects the nodes x and y directly  
+int grph[][] = new int[][] { { -1, 3, -1, -1, -1, -1, -1, 7, -1 },  
+    { 3, -1, 7, -1, -1, -1, -1, 10, 4 },  
+    { -1, 7, -1, 6, -1, 2, -1, -1, 1 },  
+    { -1, -1, 6, -1, 8, 13, -1, -1, 3 },  
+    { -1, -1, -1, 8, -1, 9, -1, -1, -1 },  
+    { -1, -1, 2, 13, 9, -1, 4, -1, 5 },  
+    { -1, -1, -1, -1, -1, 4, -1, 2, 5 },  
+    { 7, 10, -1, -1, -1, -1, 2, -1, 6 },  
+    { -1, 4, 1, 3, -1, 5, 5, 6, -1 } };  
+
+// creating an object of the class DijkstraExample  
+DijkstraExample obj = new DijkstraExample();  
+obj.dijkstra(grph, 0);  
+}  
+}