Public Class Form1
    Dim g As New Graph(5)
    Private Sub btnMakeGraph_Click(sender As Object, e As EventArgs) Handles btnMakeGraph.Click
        'Simple Graph
        g.AddVertex("A")
        g.AddVertex("B")
        g.AddVertex("C")
        g.AddVertex("D")
        g.AddVertex("E")
        g.AddEdge(0, 1, 6)
        g.AddEdge(0, 3, 1)
        g.AddEdge(1, 0, 6)
        g.AddEdge(1, 2, 5)
        g.AddEdge(1, 3, 2)
        g.AddEdge(1, 4, 2)
        g.AddEdge(2, 1, 5)
        g.AddEdge(2, 4, 5)
        g.AddEdge(3, 0, 1)
        g.AddEdge(3, 1, 2)
        g.AddEdge(3, 4, 1)
        g.AddEdge(4, 1, 2)
        g.AddEdge(4, 2, 5)
        g.AddEdge(4, 3, 1)
        MsgBox("Graph Created")
    End Sub

    Private Sub btnGetVertex_Click(sender As Object, e As EventArgs) Handles btnShowVertex.Click
        g.ShowVertex(2)
    End Sub

    Private Sub btnShowMatrix_Click(sender As Object, e As EventArgs) Handles btnShowMatrix.Click
        Dim aMatrix(4, 4) As Double
        aMatrix = g.GetAdjacencyMatrix
        Dim stOut As String
        For x As Integer = 0 To 4
            For y As Integer = 0 To 4
                stOut = stOut & aMatrix(x, y) & " "
            Next
            stOut = stOut & vbNewLine
        Next
        MsgBox(stOut)
    End Sub

    Private Sub btnGetNeighbours_Click(sender As Object, e As EventArgs) Handles btnGetNeighbours.Click
        Dim stNeighbours As String
        stNeighbours = g.GetNeighbours(Me.txtNodeId.Text)
        MsgBox(stNeighbours)
    End Sub
End Class

Public Class Vertex
    Public Value As String
    Public Sub New(ByVal Value As String)
        Me.Value = Value
    End Sub
End Class

Public Class Graph
    Private vertices() As Vertex
    Private adjacencyMatrix(,) As Double
    Private iNumberOfVertices As Integer
    Private iMaxSize As Integer
    Public Sub New(iSize As Integer)
        iMaxSize = iSize            'for use by other methods
        iSize = iSize - 1           '0 based arrays
        ReDim vertices(iSize)
        ReDim adjacencyMatrix(iSize, iSize)

        Dim x, y As Integer
        For x = 0 To iSize - 1
            For y = 0 To iSize - 1
                adjacencyMatrix(x, y) = 0
            Next
        Next
        iNumberOfVertices = 0
    End Sub

    Public Sub AddVertex(ByVal value As String)
        vertices(iNumberOfVertices) = New Vertex(value)
        iNumberOfVertices += 1
    End Sub

    Public Sub AddEdge(ByVal StartVertex As Integer, ByVal EndVertex As Integer, Weight As Double)
        adjacencyMatrix(StartVertex, EndVertex) = Weight
        adjacencyMatrix(EndVertex, StartVertex) = Weight   'undirected graph is symetrical
    End Sub

    Public Sub ShowVertex(ByVal v As Integer)
        MsgBox(vertices(v).Value)
    End Sub

    Public Function GetAdjacencyMatrix()
        Return adjacencyMatrix
    End Function

    Public Function GetNeighbours(VertexId) As String
        Dim stOut As String
        For y = 0 To iMaxSize - 1
            If adjacencyMatrix(VertexId, y) > 0 Then
                stOut = stOut & y & " "
            End If
        Next
        Return stOut
    End Function
End Class