Kosaraju's Algorithm (#598)

* Added Kosaraju's Algorithm

Added Kosaraju's Algorithm to display all the strongly connected components of a graph.

* Delete Kosaraju.java

Placed inwrong folder

* Added Kosaraju's Algorithm

Added Kosaraju's algorithm to display the strongly connected components of a graph.

* Update Kosaraju.java

Indentation

Algorithms/Kosaraju.java

@@ -0,0 +1,123 @@
+// Implementation of Kosaraju's algorithm to print all Strongly Connected Components
+
+import java.util.*;
+
+class Graph
+{
+// Adjacency List representation of Graph
+    int size; 
+	LinkedList<Integer> adjacencyList[];
+
+	Graph(int n)
+	{
+		size = n;
+		adjacencyList = new LinkedList[n];
+		for (int i=0; i<n; ++i)
+			adjacencyList[i] = new LinkedList();
+	}
+
+	void addEdge(int v, int w) 
+    { 
+        adjacencyList[v].add(w); 
+    }
+}
+public class Kosaraju
+{
+    Graph graph;
+    Kosaraju(Graph graph){
+        this.graph = graph;
+    }
+	// A recursive function to print DFS starting from v
+	void DFS(Graph g, int v,boolean visited[])
+	{
+		visited[v] = true;
+		System.out.print(v + " ");
+
+		int n;
+
+		Iterator<Integer> i = g.adjacencyList[v].iterator();
+		while (i.hasNext())
+		{
+			n = i.next();
+			if (!visited[n])
+				DFS(g, n,visited);
+		}
+	}
+
+	// Function that returns reverse of this graph
+	Graph reverse()
+	{
+		Graph rev_graph = new Graph(graph.size);
+		for (int v = 0; v < graph.size; v++)
+		{
+			Iterator<Integer> i = graph.adjacencyList[v].listIterator();
+			while(i.hasNext())
+				rev_graph.adjacencyList[i.next()].add(v);
+		}
+		return rev_graph;
+	}
+
+	void fillOrder(int v, boolean visited[], Stack stack)
+	{
+		visited[v] = true;
+
+		Iterator<Integer> i = graph.adjacencyList[v].iterator();
+		while (i.hasNext())
+		{
+			int n = i.next();
+			if(!visited[n])
+				fillOrder(n, visited, stack);
+		}
+
+		stack.push(v);
+	}
+
+	void printSCCs()
+	{
+		Stack stack = new Stack();
+
+		boolean visited[] = new boolean[graph.size];
+		for(int i = 0; i < graph.size; i++)
+			visited[i] = false;
+
+		for (int i = 0; i < graph.size; i++)
+			if (visited[i] == false)
+				fillOrder( i, visited, stack);
+
+		Graph rev_graph = reverse();
+
+		for (int i = 0; i < graph.size; i++)
+			visited[i] = false;
+
+		while (stack.empty() == false)
+		{
+			int v = (int)stack.pop();
+			if (visited[v] == false)
+			{
+				DFS(rev_graph, v, visited);
+				System.out.println();
+			}
+		}
+	}
+
+	public static void main(String args[])
+	{
+
+		Graph graph = new Graph(9);
+		graph.addEdge(0, 3);
+		graph.addEdge(1, 7);
+		graph.addEdge(2, 5);
+		graph.addEdge(3, 6);
+		graph.addEdge(4, 1);
+        	graph.addEdge(5, 8);
+        	graph.addEdge(6, 0);
+        	graph.addEdge(7, 4);
+        	graph.addEdge(7, 5);
+        	graph.addEdge(8, 6);
+        	graph.addEdge(8, 2);
+
+		System.out.println("Strongly connected components are:\n");
+		Kosaraju scc = new Kosaraju(graph);
+        	scc.printSCCs();
+	}
+}