list<Edge*>CheckList checklist;

    class Node
    {
    	//location data
    }

    class Edge
    {
    public:
    	Node* m_nA;
    	Node* m_nB;
    	Edge* m_eB;
    	bool m_IsTraced;
	bool m_IsAdded;
    }

    void AddEdge(Edge* edge, CheckList& checklist)
    {
    	for (int i = 0; i < checklist.count(); i++)
    	{
    		if (checklist.getat(i)->m_nB == edge->m_nA)
    		{
    			checklist.getat(i)->m_eB = edge;
    		}
    	}
    }

    void Build()
    {
    	for(int i = 0; i < list.count(); i++)
    	{
    		AddEdge(new Edge(list.getat[i].x1, list.getat[i].y1), CheckList& checklist);
    	}
    }

    bool DetectTrace(Edge* edge)
    {
    	if (edge->m_IsTraced)
    	{
    		edge->m_IsTraced = false;
    		return false;
    	}
    	edge->m_IsTraced = true;
    	bool returnvalue = DetectTrace(edge->m_eB);
    	edge->m_IsTraced = false;
    	return returnvalue;
    }

    void Clean()
    {
    	for (int i = 0; i < checklist.count(); i++)
    	{
    		Edge* test = checklist.getat(i);
    		if (!(test->m_isAdded)) checklist.removeat(i);
    		for (int j = 0; j < checklist.count(); j++)
    		{
    			if (checklist.getat(j)->m_eB == test) checklist.getat(j)->m_eB = null;
    		}
    	}
    }

    void Detect()
    {
    	for(int i = 0; i < checklist.count(); i++)
    	{
		checklist.getat(i)->m_IsAdded = true;
    		if (!DetectTrace(checklist.getat(i))) checklist.getat(i)->m_IsAdded = false;
    	}
    }

    int main()
    {
    	Build();
    	Detect();
    	Clean();
    	// use checklist as final collection.
    }