This linked list example implements Set abstract data type operations.

SinglyLinkedNode class

Option Explicit

Private Value As Variant
Private NextNode As SinglyLinkedNode '"Next" is a keyword in VBA and therefore is not a valid variable name

LinkedList class

Option Explicit

Private head As SinglyLinkedNode

'Set type operations

Public Sub Add(value As Variant)
    Dim node As SinglyLinkedNode
        
    Set node = New SinglyLinkedNode
    node.value = value
    Set node.nextNode = head
    
    Set head = node
End Sub

Public Sub Remove(value As Variant)
    Dim node As SinglyLinkedNode
    Dim prev As SinglyLinkedNode
    
    Set node = head
    
    While Not node Is Nothing
        If node.value = value Then
            'remove node
            If node Is head Then
                Set head = node.nextNode
            Else
                Set prev.nextNode = node.nextNode
            End If
            Exit Sub
        End If
        Set prev = node
        Set node = node.nextNode
    Wend

End Sub

Public Function Exists(value As Variant) As Boolean
    Dim node As SinglyLinkedNode
    
    Set node = head
    While Not node Is Nothing
        If node.value = value Then
            Exists = True
            Exit Function
        End If
        Set node = node.nextNode
    Wend
End Function

Public Function Count() As Long
    Dim node As SinglyLinkedNode
    
    Set node = head
    
    While Not node Is Nothing
        Count = Count + 1
        Set node = node.nextNode
    Wend
    
End Function

This is an example of an unbalanced binary search tree. A binary tree is structured conceptually as a hierarchy of nodes descending downward from a common root, where each node has two children: left and right. For example, suppose the numbers 7, 5, 9, 3, 11, 6, 12, 14 and 15 were inserted into a BinaryTree. The structure would be as below. Note that this binary tree is not balanced, which can be a desirable characteristic for guaranteeing the performance of lookups - see AVL trees for an example of a self-balancing binary search tree.

             7
            / \
           5   9
          / \   \
         3   6   11
                   \ 
                    12
                      \
                       14
                        \
                         15

BinaryTreeNode class

Option Explicit

Public left As BinaryTreeNode
Public right As BinaryTreeNode
Public key As Variant
Public value As Variant

BinaryTree class

[TODO]