Flatten binary tree in order of postorder traversal in vb.net

Vb program for Flatten binary tree in order of postorder traversal. Here more solutions.

' Include namespace system
Imports System 
'  Vb.net program for
'  Flatten binary tree in order of post-order traversal

'  Node of Binary Tree
Public Class TreeNode
    Public  data As Integer
    Public  left As TreeNode
    Public  right As TreeNode
    Public Sub New(ByVal data As Integer)
        '  Set node value
        Me.data = data
        Me.left = Nothing
        Me.right = Nothing
    End Sub
End Class

Public Class BinaryTree
    Public  root As TreeNode
    Public  back As TreeNode
    Public Sub New()
        '  Set initial tree root to null
        Me.root = Nothing
        Me.back = Nothing
    End Sub
    '  Recursive function
    '  Display postorder view of binary tree
    Public Sub postOrder(ByVal node As TreeNode)
        if (node IsNot Nothing) Then
            Me.postOrder(node.left)
            Me.postOrder(node.right)
            '  Print node value
            Console.Write(" {0} ", node.data)
        End If
    End Sub
    '  This are flattening tree nodes in postorder from
    Public Sub transform(ByVal node As TreeNode)
        if (node IsNot Nothing) Then
            '  Recursive executing left and right subtree
            Me.transform(node.left)
            Me.transform(node.right)
            if (Me.back  Is  Nothing) Then
                '  This is first node of postorder traversal
                '  Get first node of transform tree
                Me.root = node
            Else
                '  Next node
                Me.back.right = node
                '  We taking only one direction
                Me.back.left = Nothing
            End IF
            Me.back = node
        End If
    End Sub
    '  This are handling the request of
    '  flatten tree nodes in post order from.
    Public Sub flattenNode()
        if (Me.root  Is  Nothing) Then
            '  When empty tree
            Return
        End If
        '  Set back node
        Me.back = Nothing
        '  Perform flatten operation
        Me.transform(Me.root)
        if (Me.back IsNot Nothing) Then
            '  Set last node of post order
            Me.back.left = Nothing
            Me.back.right = Nothing
        End If
        Me.back = Nothing
    End Sub
    '  Display flatten elements of tree
    Public Sub showElement()
        if (Me.root  Is  Nothing) Then
            Console.WriteLine( vbLf &" Empty Tree")
            Return
        End If
        Console.WriteLine( vbLf &" Flatten Tree Node in Postorder : ")
        Dim temp As TreeNode = Me.root
        '  Iterate tree elements
        while (temp IsNot Nothing)
            '  Display node value
            Console.Write(" {0} ", temp.data)
            '  Visit to next node
            temp = temp.right
        End While
    End Sub
    Public Shared Sub Main(ByVal args As String())
        '  New tree
        Dim tree As BinaryTree = New BinaryTree()
        '    Construct Binary Tree
        '    -----------------------
        '           1
        '          / \ 
        '         /   \
        '        6     8
        '       / \   / \
        '      2   3 7   5
        '     /   /   \   \
        '    9   4    -6   11
        '  Add nodes
        tree.root = New TreeNode(1)
        tree.root.left = New TreeNode(6)
        tree.root.left.left = New TreeNode(2)
        tree.root.right = New TreeNode(8)
        tree.root.right.right = New TreeNode(5)
        tree.root.right.left = New TreeNode(7)
        tree.root.right.left.right = New TreeNode(-6)
        tree.root.left.right = New TreeNode(3)
        tree.root.left.right.left = New TreeNode(4)
        tree.root.left.left.left = New TreeNode(9)
        tree.root.right.right.right = New TreeNode(11)
        '  Display tree elements
        Console.WriteLine( vbLf &" Postorder Nodes : ")
        tree.postOrder(tree.root)
        '  Testing
        tree.flattenNode()
        '  After transform
        tree.showElement()
    End Sub
End Class

Output

 Postorder Nodes :
 9  2  4  3  6  -6  7  11  5  8  1
 Flatten Tree Node in Postorder :
 9  2  4  3  6  -6  7  11  5  8  1