How to implement a Non-Binary tree

Question

I am having trouble implementing a non-binary tree, where the root node can have an arbitrary amount of child nodes. Basically, I would like some ideas on how where to go with this, since I do have some code written, yet I'm stuck at this point on what to do next. BTW I cannot use any of the Collections classes at all. I can only use System.

using System;

namespace alternate_solution
{
 //            [root]
 //        /  /      \    \
 //    text  text  text  text

class Node//not of type TreeNode (since Node is different from TreeNode)
{
    public string data;
    public Node child;

    public Node(string data)
    {
        this.data = data;
        this.child = null;
    }

}

}

Answer 1

So far Jerska's solution is the best but it is needlessly complicated.

Since I assume this is a homework exercise let me give you the direction you should head in. The data structure you want is:

class TreeNode
{
  public string Data { get; private set; }
  public TreeNode FirstChild { get; private set; }
  public TreeNode NextSibling { get; private set; }
  public TreeNode (string data, TreeNode firstChild, TreeNode nextSibling)
  {
    this.Data = data;
    this.FirstChild = firstChild;
    this.NextSibling = nextSibling;
  }
}

Let's now redraw your diagram -- vertical lines are "first child", horizontal lines are "next sibling"

Root
 |
 p1 ----- p2 ----- p4 ----- p6  
 |        |         |       |
 c1       p3       c4       p7
          |                 |
          c2 - c3           c5

Make sense?

Now, can you write code that produces this tree using this data structure? Start from the rightmost leaves and work your way towards the root:

TreeNode c5 = new TreeNode("c5", null, null);
TreeNode p7 = new TreeNode("p7", c5, null);
TreeNode p6 = new TreeNode("p6", p6, null);
... you do the rest ...

Notice that an arbitrary tree is just a binary tree "rotated 45 degrees", where the root never has a "right" child. Binary trees and arbitrary trees are the same thing; you just assign different meanings to the two children.

Answer 2

Since you can't use a collection, why don't you create your own list ?

class Child {
    Node node;
    Child next = null;

    public Child (Node node) {
        this.node = node;
    }

    public void addChild (Node node) {
        if (this.next == null)
            this.next = new Child (node);
        else
            this.next.addChild (node);
    }
}

class Node {
   public string data;
   public Child children = null;

   public Node (string data) {
       this.data = data;
   }

   public void addChild (Node node) {
       if (this.children == null)
           this.children = new Child (node);
       else
           this.children.addChild (node);
   }
}

And use it like this :

Node root = new Node ("Hey");
root.addChild (new Node ("you"));
root.addChild (new Node ("me"));

You'll now have :

          Node ("Hey")
        /             \
   Node ("you")     Node ("me")

Then you will need to implement different functions (getters, removers, etc.). But that's your job.

Answer 3

If you can't use any Collections, store link in all child elements to parent. You can model your graph by using next data structure:

class Node
{
    public string Data { get; set; }
    public Node Parent { get; set; }

    public Node(string data, Node parent)
    {
        Data = data;
        Parent = parent;
    }
}

You can now have as many childs for each node, as you like:

var root = new Node("root", null);

var parent = new Node("parent", root);
var anotherParent = new Node("yetAnotherParent", root);

var child = new Node("Child", parent);
var anotherchild = new Node("anotherchild", parent);