Java Program to Detect Cycle in a Directed Graph

Last Updated : 02 Jan, 2019

Given a directed graph, check whether the graph contains a cycle or not. Your function should return true if the given graph contains at least one cycle, else return false. For example, the following graph contains three cycles 0->2->0, 0->1->2->0 and 3->3, so your function must return true.

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Java

// A 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<>()); 
    } 
  
    // This function is a variation of DFSUytil() in 
    // https:// www.geeksforgeeks.org/archives/18212 
    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. 
    // This function is a variation of DFS() in 
    // https:// www.geeksforgeeks.org/archives/18212 
    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; 
    } 
  
    // Driver code 
    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"); 
    } 
} 
  
// This code is contributed by Sagar Shah. 

Output:

Graph contains cycle

Please refer complete article on Detect Cycle in a Directed Graph for more details!

Suggest improvement

Java Program for Print Number series without using any loop

Java Program for Egg Dropping Puzzle | DP-11

Share your thoughts in the comments

Java Program to Detect Cycle in a Directed Graph

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Java

Please Login to comment...

Similar Reads

What kind of Experience do you want to share?