Detecting Cycles in a Directed Graph

Question

Can somebody help me how to find cycles in a directed graph,
I already made a Depth First Search code and base on what I've learned Cycles can be done using Depth First Search
public static void DFS(int numberNodes){
    System.out.print("Enter starting node for Depth First search: ");
        int v = scanner.nextInt();
    for(int i = 1;i<=numberNodes;i++)
             visited[i] = false;
        dfs_rec(v,numberNodes);
    }//end DFS()
     public static void dfs_rec(int v,int n){
    int i;
    visited[v] = true;     
         System.out.print(" "+v);
         for(i = 1;i<n;i++)
              if(adj[v] == 1 && visited[i] == false)
               dfs_rec(i,n);
     }//end dfs rec                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

Answer 1

malcolmmc wrote:
paulcw wrote:
I don't see the need for unsetting the flag. Visited is visited. What needs to be added is to respond when the flag is set to true.You need to clear the flag because the same node might be reached through more than one route without the graph being cyclic (it could be a shared sub-tree).
Only if you encounter a node which is already part of the path you're examining have you found a loop.But not if it's a depth-first search, no?
Oh, I see what you're saying. Set the flag, do a depth-first search, then when you exhaust that and do a sibling, clear the flag. OK.