VB.NET exercises and solutions: add element to linked list


Singly linked list

Add element to singly linked list

Step 2: Add an element to the linked list

To add an element to the linked list, you need to consider 4 things:

1. When the list is empty, to add a new element to the list, you only let the pfirst and plast links point to the new item. We mark the Nothing value of link of an element by crossed lines.

Add an item to the empty list  

2.If the new element is to be added to the beginning of  the list, you will need to let the link of the new item points to the pfirst and then update the pfirst to point to the new item.

Add a new element at the beginning of the list  

 3. If the new element is to be added to the middle position of the list, you need to let a link point to the position immediately before the position that the new element will be placed in.

Add a new item in the middle of the list  

4. If the new element is to be added to the last of the list, you need to let the link of the plast point to the new element then update the plast to point the new element.

Add the new item to the last of the list  

'VB.NET code to insert a new item to the linkedlist

Public Overrides Sub insert(ByVal val As Integer, ByVal pos As Integer)

Dim newnode As ListNode = New ListNode(val)
'empty list


If IsNothing(pfirst) And IsNothing(plast) Then

 newnode.nextlk = Nothing
 pfirst = newnode
 plast = newnode
 Console.WriteLine("Inserted:{0}", newnode.val)

'Insert at the beginning of the LinkedList
 ElseIf (pos = 1) Then

  newnode.nextlk = pfirst
  pfirst = newnode
  Console.WriteLine("Inserted:{0}", newnode.val)

'Insert in the middle of the list
  ElseIf (pos > 1 And pos <= countitem()) Then

   Dim ta As ListNode
   Dim t As Integer
   ta = pfirst
   For t = 1 To pos - 1
   ta = ta.nextlk
   Next
   newnode.nextlk = ta.nextlk
   ta.nextlk = newnode
   Console.WriteLine("Inserted:{0}", newnode.val)

 ElseIf (pos = countitem() + 1) Then

  newnode.nextlk = Nothing 'The next link of the item is null.
  plast.nextlk = newnode
  plast = newnode
  Console.WriteLine("Inserted:{0}", newnode.val)


 Else : Console.WriteLine("Invalid position!")
 End If


End Sub



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