Remove duplicate characters from strings and find the shortest

Question

I can not figure out how to select from the result or the shortest line itself or its number

(Yes, the solution is needed in such ancient operators)

Imports System.IO
Public Class Form1
    Sub readputh(ByRef s As String)
        s = ""
        OpenFileDialog1.Filter = "Textfiles (*.txt)|*.txt"
        OpenFileDialog1.ShowDialog()
        Do While s = ""
            s = OpenFileDialog1.FileName
        Loop
    End Sub
    Sub writeputh(ByRef s As String)
        s = ""
        SaveFileDialog1.Filter = "Textfiles (*.txt)|*.txt"
        SaveFileDialog1.ShowDialog()
        Do While s = ""
            s = SaveFileDialog1.FileName
        Loop
    End Sub

    Sub ch(ByVal Str As String, ByRef Res As String)
        Dim a As Char
        Res = Mid(Str, 1, 1)
        For i = 2 To Len(Str)
            a = CChar(Mid(Str, i, 1))
            If InStr(Res, a) = 0 Then
                Res = Res + a
            End If
        Next
    End Sub

    Sub resh(ByVal filename1 As String, ByVal filename2 As String, ByRef lb1 As ListBox, ByRef lb2 As ListBox)
        Dim rf As StreamReader
        Dim wf As StreamWriter
        Dim s1, s2, s3 As String
        s2 = ""
        s3 = ""
        Try
            rf = New StreamReader(filename1)
            wf = New StreamWriter(filename2, True)
            Do While Not rf.EndOfStream()
                s1 = rf.ReadLine()
                lb1.Items.Add(s1)
                ch(s1, s2)
                wf.WriteLine(s2)
                lb2.Items.Add(s2)
            Loop
            wf.Close()
            rf.Close()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim filename1, filename2 As String
        readputh(filename1)
        writeputh(filename2)
        resh(filename1, filename2, ListBox1, ListBox2)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        End
    End Sub
End Class

Input file: youtubeyoutubeyotube dogdogdogdog geeksforgeeks

Output file: youtbe dog geksfor

But I expect Output file of only "dog"

Answer 1

I just couldn't handle the old code. One based functions? No! You can translate it back it you want but output is now dog.

Private Function GetOpenPath() As String
    OpenFileDialog1.Filter = "Textfiles (*.txt)|*.txt"
    If OpenFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
        Return OpenFileDialog1.FileName
    Else
        Return Nothing
    End If
End Function

Private Function GetSavePath() As String
    SaveFileDialog1.Filter = "Textfiles (*.txt)|*.txt"
    If SaveFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
        Return SaveFileDialog1.FileName
    Else
        Return Nothing
    End If
End Function

Private Function ch(ByVal Str As String) As String
    Dim a As Char
    Dim Res = Str.Substring(0, 1)
    For i = 1 To Str.Length - 1
        a = CChar(Str.Substring(i, 1))
        If Res.IndexOf(a) = -1 Then
            Res &= a
        End If
    Next
    Return Res
End Function

Sub resh(ByVal filename1 As String, ByVal filename2 As String)
    Dim lines = File.ReadAllLines(filename1)         
    Dim NewLines As New List(Of String)
    For Each line In lines
        Try
            ListBox1.Items.Add(line)
            Dim s2 = ch(line)
            NewLines.Add(s2)
            ListBox2.Items.Add(s2)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    Next
    Dim Shortest = NewLines.OrderByDescending(Function(s) s.Length).Last()
    File.WriteAllText(filename2, Shortest)
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim OpenPath = GetOpenPath()
    Dim SavePath = GetSavePath()
    If String.IsNullOrEmpty(OpenPath) OrElse String.IsNullOrEmpty(SavePath) Then
        MessageBox.Show("You must provide a file. Try again.")
        Return
    End If
    resh(OpenPath, SavePath)
End Sub