Tree data structure in C#

Question

I was looking for a tree or graph data structure in C# but I guess there isn't one provided. An Extensive Examination of Data Structures Using C# 2.0 explains a bit about why. Is there a convenient library which is commonly used to provide this functionality? Perhaps through a strategy pattern to solve the issues presented in the article.

I feel a bit silly implementing my own tree, just as I would implementing my own ArrayList.

I just want a generic tree which can be unbalanced. Think of a directory tree. C5 looks nifty, but their tree structures seem to be implemented as balanced red-black trees better suited to search than representing a hierarchy of nodes.

Answer 1

Here's a Tree

public class Tree<T> : List<Tree<T>>
{
    public  T Data { get; private set; }

    public Tree(T data)
    {
        this.Data = data;
    }

    public Tree<T> Add(T data)
    {
        var node = new Tree<T>(data);
        this.Add(node);
        return node;
    }
}

You can even use initializers:

    var tree = new Tree<string>("root")
    {
        new Tree<string>("sample")
        {
            "console1"
        }
    };

Answer 2

I hate to admit it but I ended up writing my own tree class using a linked list. On an unrelated note I just discovered this round thing which, when attached to a thing I'm calling an 'axle' allows for easier transportation of goods.

Answer 3

Because it isn't mentioned I would like you draw attention the now released .net code-base: specifically the code for a SortedSet that implements a Red-Black-Tree:

https://github.com/Microsoft/referencesource/blob/master/System/compmod/system/collections/generic/sortedset.cs

This is, however, a balanced tree structure. So my answer is more a reference to what I believe is the only native tree-structure in the .net core library.

Answer 4

Here's my own:

class Program
{
    static void Main(string[] args)
    {
        var tree = new Tree<string>()
            .Begin("Fastfood")
                .Begin("Pizza")
                    .Add("Margherita")
                    .Add("Marinara")
                .End()
                .Begin("Burger")
                    .Add("Cheese burger")
                    .Add("Chili burger")
                    .Add("Rice burger")
                .End()
            .End();

        tree.Nodes.ForEach(p => PrintNode(p, 0));
        Console.ReadKey();
    }

    static void PrintNode<T>(TreeNode<T> node, int level)
    {
        Console.WriteLine("{0}{1}", new string(' ', level * 3), node.Value);
        level++;
        node.Children.ForEach(p => PrintNode(p, level));
    }
}

public class Tree<T>
{
    private Stack<TreeNode<T>> m_Stack = new Stack<TreeNode<T>>();

    public List<TreeNode<T>> Nodes { get; } = new List<TreeNode<T>>();

    public Tree<T> Begin(T val)
    {
        if (m_Stack.Count == 0)
        {
            var node = new TreeNode<T>(val, null);
            Nodes.Add(node);
            m_Stack.Push(node);
        }
        else
        {
            var node = m_Stack.Peek().Add(val);
            m_Stack.Push(node);
        }

        return this;
    }

    public Tree<T> Add(T val)
    {
        m_Stack.Peek().Add(val);
        return this;
    }

    public Tree<T> End()
    {
        m_Stack.Pop();
        return this;
    }
}

public class TreeNode<T>
{
    public T Value { get; }
    public TreeNode<T> Parent { get; }
    public List<TreeNode<T>> Children { get; }

    public TreeNode(T val, TreeNode<T> parent)
    {
        Value = val;
        Parent = parent;
        Children = new List<TreeNode<T>>();
    }

    public TreeNode<T> Add(T val)
    {
        var node = new TreeNode<T>(val, this);
        Children.Add(node);
        return node;
    }
}

Output:

Fastfood
   Pizza
      Margherita
      Marinara
   Burger
      Cheese burger
      Chili burger
      Rice burger

Answer 5

Yet another tree structure:

public class TreeNode<T> : IEnumerable<TreeNode<T>>
{

    public T Data { get; set; }
    public TreeNode<T> Parent { get; set; }
    public ICollection<TreeNode<T>> Children { get; set; }

    public TreeNode(T data)
    {
        this.Data = data;
        this.Children = new LinkedList<TreeNode<T>>();
    }

    public TreeNode<T> AddChild(T child)
    {
        TreeNode<T> childNode = new TreeNode<T>(child) { Parent = this };
        this.Children.Add(childNode);
        return childNode;
    }

    ... // for iterator details see below link
}

Sample usage:

TreeNode<string> root = new TreeNode<string>("root");
{
    TreeNode<string> node0 = root.AddChild("node0");
    TreeNode<string> node1 = root.AddChild("node1");
    TreeNode<string> node2 = root.AddChild("node2");
    {
        TreeNode<string> node20 = node2.AddChild(null);
        TreeNode<string> node21 = node2.AddChild("node21");
        {
            TreeNode<string> node210 = node21.AddChild("node210");
            TreeNode<string> node211 = node21.AddChild("node211");
        }
    }
    TreeNode<string> node3 = root.AddChild("node3");
    {
        TreeNode<string> node30 = node3.AddChild("node30");
    }
}

BONUS
See fully-fledged tree with:

• iterator
• searching
• Java/C#

https://github.com/gt4dev/yet-another-tree-structure

Answer 6

I create a Node class that could be helpfull for other people. The class has properties like:

• Children
• Ancestors
• Descendants
• Siblings
• Level of the node
• Parent
• Root
• Etc.

There is also the possibility to convert a flat list of items with an Id and a ParentId to a tree. The nodes holds a reference to both the children and the parent, so that makes iterating nodes quite fast.