Question

I have tree node defined like this:

class TreeNode : IEnumerable<TreeNode>
{
    private readonly Dictionary<string, TreeNode> _childs = new Dictionary<string, TreeNode>();

    public readonly string ID;

    public TreeNode Parent { get; private set; }

    public int Level { get; set; }

    public TreeNode(string id)
    {
        this.ID = id;
    }
    // some other methods
}

I created tree from keywords by this and now I have sometimes branch where parent tree node has one child and that child could have one child too and after some nodes there are 2 childs. So I want now to reduce all that one child (remove it) to “level” where there are at least 2 child nodes.

I tried something like this:

private void TreeReduction(TreeNode node)
    {
        while (node.Count() == 1)
        {
            node = node.GetFirstChild();
        }
        foreach (var child in node)
        {
            TreeReduction(child);
        }
    }

and I call it to main node. It’s look okay and it’s going through tree but that nodes aren’t rewrite. I tried out parameter for treenode but I have problem with foreach loop. How can I fix it to have it working? Thanks

Answer 1

Making many assumptions about what would happen, for example to single-branch single-leaf tree, you could go for something like this.

var redux = TreeReduction(rootNode, 0);

Aside this, the key point is for your recursive method to return a TreeNode which you will be able to set as childnode.

I Left out the Parent property as its setter is private. If AddChild does not set it, you should make it public and carry it as a parameter.

private TreeNode TreeReduction(TreeNode node, int currentLevel)
    {
        if(node==null)
          return null;
        if(node.Count() == 1)
        {
            var redux = TreeReduction(node.GetFirstChild(), currentLevel);
            return redux?? new TreeNode(node.ID{level=currentLevel});
        }
        var newNode = new TreeNode(node.ID{level=currentLevel});
        foreach (var child in node)
        {
            var newChild = TreeReduction(child, currentLevel+1);
            if(newChild!=null)
               newNode.AddChild(newChild);
        }
        return newNode;
    }