#define DIGITS  "0123456789"

' Funciones que agraga un elemento a un array dinámico
Sub AddToArray(arr() As Byte, value As Byte)
    Redim Preserve arr(Ubound(arr) + 1)
    arr(Ubound(arr)) = value
End Sub
Sub AddToArrayString(arr() As String, value As String)
    Redim Preserve arr(Ubound(arr) + 1)
    arr(Ubound(arr)) = value
End Sub

Sub DeBruijnHelper(k As Integer, n As Integer, a() As Byte, seq() As Byte, t As Integer, p As Integer)
    Dim As Integer i, j
    If t > n Then
        If n Mod p = 0 Then
            For i = 1 To p
                Redim Preserve seq(Ubound(seq) + 1)
                seq(Ubound(seq)) = a(i)
            Next
        End If
    Else
        a(t) = a(t - p)
        DeBruijnHelper(k, n, a(), seq(), t + 1, p)
        j = a(t - p) + 1
        While j < k
            a(t) = j
            DeBruijnHelper(k, n, a(), seq(), t + 1, t)
            j += 1
        Wend
    End If
End Sub

Function DeBruijn(k As Integer, n As Integer) As String
    Dim As String alphabet = Left(DIGITS, k)
    Dim As Byte a(k * n)
    Dim As Byte seq()
    DeBruijnHelper(k, n, a(), seq(), 1, 1)

    Dim As String buf = ""
    For i As Integer = 0 To Ubound(seq)
        buf &= Mid(alphabet, seq(i) + 1, 1)
    Next
    Dim As String b = buf

    Return b & Left(b, n - 1)
End Function

Function AllDigits(s As String) As Boolean
    For i As Integer = 1 To Len(s)
        Dim c As String = Mid(s, i, 1)
        If c < "0" Orelse c > "9" Then Return False
    Next
    Return True
End Function

Sub Validate(db As String)
    Dim As Integer i, n, lerr
    Dim As Integer le = Len(db)
    Dim As Integer found(9999)
    Dim As String errs()
    Dim As String s
    ' Check all strings of 4 consecutive digits within 'db'
    ' to see if all 10,000 combinations occur without duplication.
    For i = 1 To le - 3
        s = Mid(db, i, 4)
        If AllDigits(s) Then
            n = Val(s)
            found(n) += 1
        End If
    Next
    For i = 0 To 9999
        If found(i) = 0 Then
            Redim Preserve errs(Ubound(errs) + 1)
            errs(Ubound(errs)) = "    PIN number " & Right("0000" & i, 4) & " missing"
        Elseif found(i) > 1 Then
            Redim Preserve errs(Ubound(errs) + 1)
            errs(Ubound(errs)) = "    PIN number " & Right("0000" & i, 4) & " occurs " & found(i) & " times"
        End If
    Next

    lerr = Ubound(errs) + 1
    If lerr = 0 Then
        Print "  No errors found"
    Else
        s = Iif(lerr = 1, "", "s")
        Print "  "; lerr; " error"; s; " found:"
        For i = 0 To Ubound(errs)
            Print errs(i)
        Next
    End If
End Sub

Function Reverse(s As String) As String
    Dim As Integer i
    Dim As String arr()
    For i = 1 To Len(s)
        Redim Preserve arr(Ubound(arr) + 1)
        arr(Ubound(arr)) = Mid(s, i, 1)
    Next
    Dim rev As String = ""
    For i = Ubound(arr) To 0 Step -1
        rev &= arr(i)
    Next
    Return rev
End Function

Sub main()
    Dim As String bytes()
    Dim As String db = DeBruijn(10, 4)
    Dim As Integer i, le = Len(db)

    Print "The length of the de Bruijn sequence is "; le
    Print !"\nThe first 130 digits of the de Bruijn sequence are: "; Left(db, 130)
    Print !"\nThe last 130 digits of the de Bruijn sequence are: "; Mid(db, le - 129, 130)
    Print !"\nValidating the deBruijn sequence:"
    Validate(db)
    Print !"\nValidating the reversed deBruijn sequence:"
    Validate(Reverse(db))

    For i = 1 To Len(db)
        Redim Preserve bytes(Ubound(bytes) + 1)
        bytes(Ubound(bytes)) = Mid(db, i, 1)
    Next
    bytes(4443) = "."
    db = ""
    For i = 0 To Ubound(bytes)
        db &= bytes(i)
    Next
    Print !"\nValidating the overlaid deBruijn sequence:"
    Validate(db)
End Sub

main()
Sleep