Question

I have a small problem and I would like to get your opinion.

I’m dealing with documents than can reference other documents. Starting from any document, I need to get the id of all the documents this document references. The problem is that the circular references are allowed so if A ref B ref C, again C can ref A and I get in the loop.
How can I solve this problem in C#?

An small example:

Let suppose that this is a class that represents a document:

public class Document
{
    public Document(int id)
    {
        this.ID = id;
    }

    private int m_ID;

    public int ID
    {
        get { return m_ID; }
        set { m_ID = value; }
    }

    private List<Document> m_Children = new List<Document>();

    public List<Document> Children
    {
        get { return m_Children; }
        set { m_Children = value; }
    }

    private List<Document> m_Parent = new List<Document>();

    public List<Document> Parent
    {
        get { return m_Parent; }
        set { m_Parent = value; }
    }

    public Document AddChild(Document child)
    {
        child.Parent.Add(this);
        this.Children.Add(child);

        return child;
    }

    public Document AddChild(int child)
    {
        Document d = new Document(child);

        return AddChild(d);
    }
}

Now let’s create a Document class that has some references:

public static Document CreateReferences()
{
    Document d = new Document(1);

    Document temp = d.AddChild(2);

    for (int i = 3; i < 6; i++)
    {
        temp = temp.AddChild(i);
    }

    temp.AddChild(d);

    return d;
}

Now I need to implement a method in Document class like

public List<int> GetReferencedDocuments()
{    }

What is the best way to do that? Any specific algorithm can be implemented?

Any suggestion is well accepted!

Thanks

Answer 1

Any tree-traversal algorithm would be fine.

---

As well as a list of docs you’re going to build up, maintain a queue of documents you’ve yet to check, add the first document to that list.

Then, while the queue isn’t empty, get the next doc, if it’s not already in your list, then add it, and add all referenced docs to your queue.

---

List<Document> FoundDocs = new List<Documents();
Queue<Document> DocsToSearch = new Queue<Document>();

DocsToSearch.Enqueue(StartDoc);

while(DocsToSearch.Count != 0)
{
    Document Doc = DocsToSearch.Dequeue();
    if(!FoundDocs.Contains(Doc))
    {
        FoundDocs.Add(Doc);
        foreach(var ChildDoc in Doc.Children)
        {
            DocsToSearch.Enqueue(ChildDoc);
        }
    }
}