added cycle detection in directed graph program

Author: arorayash

Graph/Detect_Cycle/detect_cycle_directed.java

@@ -0,0 +1,86 @@
+// Java Program to detect cycle in a graph 
+import java.util.ArrayList; 
+import java.util.LinkedList; 
+import java.util.List; 
+
+class Graph { 
+	
+	private final int V; 
+	private final List<List<Integer>> adj; 
+
+	public Graph(int V) 
+	{ 
+		this.V = V; 
+		adj = new ArrayList<>(V); 
+		
+		for (int i = 0; i < V; i++) 
+			adj.add(new LinkedList<>()); 
+	} 
+	
+	private boolean isCyclicUtil(int i, boolean[] visited, 
+									boolean[] recStack) 
+	{ 
+		
+		// Mark the current node as visited and 
+		// part of recursion stack 
+		if (recStack[i]) 
+			return true; 
+
+		if (visited[i]) 
+			return false; 
+			
+		visited[i] = true; 
+
+		recStack[i] = true; 
+		List<Integer> children = adj.get(i); 
+		
+		for (Integer c: children) 
+			if (isCyclicUtil(c, visited, recStack)) 
+				return true; 
+				
+		recStack[i] = false; 
+
+		return false; 
+	} 
+
+	private void addEdge(int source, int dest) { 
+		adj.get(source).add(dest); 
+	} 
+
+	// Returns true if the graph contains a 
+	// cycle, else false. 
+	private boolean isCyclic() 
+	{ 
+		
+		// Mark all the vertices as not visited and 
+		// not part of recursion stack 
+		boolean[] visited = new boolean[V]; 
+		boolean[] recStack = new boolean[V]; 
+		
+		
+		// Call the recursive helper function to 
+		// detect cycle in different DFS trees 
+		for (int i = 0; i < V; i++) 
+			if (isCyclicUtil(i, visited, recStack)) 
+				return true; 
+
+		return false; 
+	} 
+
+	public static void main(String[] args) 
+	{ 
+		Graph graph = new Graph(4); 
+		graph.addEdge(0, 1); 
+		graph.addEdge(0, 2); 
+		graph.addEdge(1, 2); 
+		graph.addEdge(2, 0); 
+		graph.addEdge(2, 3); 
+		graph.addEdge(3, 3); 
+		
+		if(graph.isCyclic()) 
+			System.out.println("Graph contains cycle"); 
+		else
+			System.out.println("Graph doesn't "
+									+ "contain cycle"); 
+	} 
+}