# Data Structures
[TODO: This topic should be an example of all the basic CS 101 data structures along with some explanation as an overview of how data structures can be implemented in VBA. This would be a good opportunity to tie in and reinforce concepts introduced in Class-related topics in VBA documentation.]
# Linked List
This linked list example implements Set abstract data type (opens new window) operations.
Option Explicit Private Value As Variant Private NextNode As SinglyLinkedNode '"Next" is a keyword in VBA and therefore is not a valid variable name
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
# Binary Tree
This is an example of an unbalanced binary search tree (opens new window). 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 (opens new window), which can be a desirable characteristic for guaranteeing the performance of lookups - see AVL trees (opens new window) for an example of a self-balancing binary search tree.
7 / \ 5 9 / \ \ 3 6 11 \ 12 \ 14 \ 15
Option Explicit Public left As BinaryTreeNode Public right As BinaryTreeNode Public key As Variant Public value As Variant