Number of Nodes in a Cycle of a graph

Question

I am trying to find the number of nodes in a cycle of a graph. I am using recursion and DFS to calculate the number of nodes in all the cycles of the graph.Here is the calculating function in C++.

int iscyclic(int node,bool visited[],bool rec[],vector<int>g[])
{
    if(!visited[node])
{
    visited[node] = true;
    rec[node] = true;
    vector<int>::iterator it;
    for(it=g[node].begin();it!=g[node].end();it++)
    {
        if(!visited[*it] && iscyclic(*it,visited,rec,g))
        {
            kount++;
        }
        else if(rec[*it])
            kount++;
    }
}
rec[node] = false;
return kount;
}

The Visited and rec array are set to false by default and kount has been globally set as 0 . The kount is supposed to calculate the number of nodes in a cycle of the directed graph.However there are cases where the answer is wrong. Please help.I Have recently started learning graph theory.

Answer 1

You should not do this:

else if(rec[*it])
   kount++;

Also, you need to make sure that the starting node (the one you call the function with) is really part of a cycle.

Third thing - you return kcount as result of your function, when you atually should return true or false based on the fact whether you encountered a cycle in this branch or not.