Dijkstra’s shortest path algorithm

Author: mr-siddy

Dijkstra’s shortest path algorithm

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+
+// 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 = 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); 
+	} 
+} 
+