How do you fill up a directed depth first search with the time which came and time at which it left?

Question

How do you fill up a directed depth first search with the time which came and time at which it left? Does it matter whether its direct or undirected for DFS?

for example

Answer 1

You simply keep a counter and assign-and-increase it each time you start and finish the DFS on a node. As the node to choose for starting the DFS of your picture (as it visits all the nodes in the graph and not just the ones connected to the U node), you would have to create a fake node that is connected to all the nodes in the graph and call the DFS on that node.

int time = 0;
HashSet<Vertex> visited = new HashSet<>();

DFS(Vertex v){
    v.start = time++;
    v.end = Integer.MAX_VALUE;
    for(Vertex t : v.neighbors){
        if(!visited.contains(t)){
            visited.add(t);
            DFS(t)
        }
        else if(t.start < v.start && t.end < v.start)
            //cross edge
        else if(t.start < v.start)
            //back edge
        else if(t.start > v.start)
            //forward edge

    }
    v.end = time++;
}