How To Find Duplicates In String

I am trying to find duplicates in a string. The code works more than I would. The purpose is to create a jagged array with values and positions like this one:

myString = "1123464263948465475965069068547363532627281901"
jagged= {{{1},{0,1,42,45}},{{2},{2,7,36,38,40}},{{3},{3,9,31,33,35}},{{4},{4,6,11,13,16,29}},.........}

Value Positions
1 0,1,42,45
2 2,7,36,38,40
3 3,9,31,33,35
4 4,6,11,13,16,29 ......... and so on with unique keys and multiple or not values.

My code do this, but looping all over the string there a moment when it repeats values and positions, because already found them earlier. How do I make to keep just the UNIQUES? How do I skip the loop when the value is already in?

My code below
Public Class Form1
Public myString As String = " "
Public jagged()() As Integer
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
myString = "1123464263948465475965069068547363532627281901"
jagged = New Integer(myString.Length - 1)() {}
[Code] .....