Deel een getal door allemaal priemgetallen. [vb.net]

[Mr Wolf]

Deel een getal door allemaal priemgetallen.

Voorbeeld:
vul 120 in
druk op bereken
En je ziet dat
2*2*2*3*5 = 120
2, 3 en 5 zijn priemgetallen.

Volgens mijn wiskundeboek wordt dit veel gebruikt bij internetbankieren.

Hieronder staat de vb.net code, en daaronder een zip met het programma er in.

Public Class Form1
    Private Function GetDivisionNumber(ByVal n As Integer) As Integer
        If n Mod 2 = 0 And n <> 2 Then
            GetDivisionNumber = 2
            Exit Function
        Else
            For i As Integer = 3 To n / 2 Step 2
                If n Mod i = 0 Then
                    GetDivisionNumber = i
                    Exit Function
                End If
            Next
        End If
        GetDivisionNumber = -1
    End Function

    Private Function PartByPrimes(ByVal n) As List(Of Integer)
_start:
        Dim rList As New List(Of Integer)
        Dim startIndex As Integer = 3
        If GetDivisionNumber(n) = -1 Then
            rList.Add(n)
            PartByPrimes = rList
            Exit Function
        End If

        If n Mod 2 = 0 Then
            Dim r As Integer = n / 2
            rList.Add(2)
            rList.AddRange(PartByPrimes(r))
            startIndex = 2
            GoTo _end
        End If

        For i As Integer = startIndex To n / 2 Step 2
            If n Mod i = 0 Then
                If GetDivisionNumber(i) = -1 Then
                    Dim r As Integer = n / i
                    rList.Add(i)
                    rList.AddRange(PartByPrimes(r))
                    startIndex = i
                    GoTo _end
                End If
            End If
        Next
_end:
        Dim cN As Integer
        For Each x As Integer In rList
            If cN = Nothing Then
                cN = x
            Else
                cN *= x
            End If
        Next
        If cN <> n Then
            If startIndex > n / 2 - 2 Then
                rList.Clear()
                PartByPrimes = rList
                Exit Function
            End If
            rList.Clear()
            GoTo _start
        End If
        PartByPrimes = rList
    End Function

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            ListBox1.Items.Clear()
            Dim dN As Integer = 1
            Dim l As List(Of Integer) = PartByPrimes(NumericUpDown1.Value)

            For Each x As Integer In l
                ListBox1.Items.Add(x.ToString + " * " + dN.ToString + " = " + (dN * x).ToString)
                dN *= x
            Next
        Catch ex As Exception
            ListBox1.Items.Clear()
            ListBox1.Items.Add("MISLUKT")
        End Try
    End Sub

    Private Sub NumericUpDown1_ValueChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NumericUpDown1.ValueChanged
        NumericUpDown1.Value = Math.Round(NumericUpDown1.Value, MidpointRounding.AwayFromZero)
    End Sub
End Class

Mr. Wolf