Simple Linked List C# AddAfter method

Question

Im working with simple linked lists in C# and I have no idea how to add elements at the end of the list, colud anyone helpme?

namespace ConsoleApplication1
{
    class Class1
    {
        public class Node()
        {
            public int Data;
            public Node Next;
        }

        private Node FirstNode=null;

        public void AddBefore(int number)        
        {
            Node NewNode=new Node();

            NewNode.Next=FirstNode;
            NewNode.Data=number;

            FirstNode=NewNode;

        }

        public void AddAfter(int number)
        {
            if (FirstNode==null)
            {
                AddBefore(number);
            }
            else
            {                    
                ???????????????
            }
        } 
     }
} 

Answer 1

The question is kind of confusing. Are you asking how to place a node at the end of the list, or as the next item in the list.

I had to do this for a homework assignment way back in the day (it was java though). If you want to always add a node to the end of the list then you also need to edit your list class to contain a head and tail of the list. This will allow you to add items to the end or beginning.

If you want to always add a node to the end then you could try editing the code so that when you add a node to the end the previous node's next node value will be set to the tail instead of null. This will always allow for you to add an item to the end of the list (which is what most add methods do unless a position is specified anyways)

In short: Add Node tailNode = null; to Class and add a method that will get and set the next node for the Node class. Once this is done, then edit the code so that it looks something like this:

class Class1
{
    public class Node()
    {
        public int Data;
        public Node Next;

        //Class to set next node
        public void setNext(Node nextNode)
        {
           //Set next node
           Next = nextNode;
        }

        //Get next node
        public Node getNext()
        { 
           return Next;
        }

    }

    private Node FirstNode=null;
    private Node lastNode = null;

    public void AddBefore(int number)        
    {
        Node NewNode=new Node();

        NewNode.Next=FirstNode;
        NewNode.Data=number;

        FirstNode=NewNode;

    }

    public void AddAfter(int number)
    {
        if (FirstNode==null)
        {
            AddBefore(number);
        }
        else
        {                    
            if(FirstNode.getNext() == null)
            {
               //No tail. Make this node tail
               lastNode = new Node();
               lastNode.Data = number;
               //Set first node's next to last node
               FirstNode.setNext(lastNode);
            }else{ //TailNode already set
               //New node to be tail
               Node newLastNode = new Node();
               newLastNode.Data = number;
               //Set the current tail node to have this node as next
               lastNode.setNext(newLastNode);
               //Make new last node last node
               lastNode = newLastNode;

            }
        }
    } 
 }

The code may be a little off (I haven't really tested it) but that is the main picture of what you are going to have to do.

Answer 2

You need to iterate through your list until you find the last node, and then add it to the end. Something like:

    public void AddAfter(int number)
    {
        if (FirstNode==null)
        {
            AddBefore(number);
        }
        else
        {
            // Finding the last node
            Node currentNode = FirstNode;
            while (currentNode.NextNode != null)
                currentNode = currentNode.NextNode;

            // Constructing a new node
            Node newNode = new Node();
            newNode.Data = number;
            newNode.Next = null;

            // Adding the new node to the end
            currentNode.NextNode = newNode;
        }
    } 

Answer 3

else
{                    
    Node NewNode=new Node();
    NewNode.Data=number;
    Node LastNode = GetLastNode();
    LastNode.Next = NewNode;
}

You'll still have to implement GetLastNode or else you wont practise anything =P