Function LCS(a As String, b As String) As String
    Dim As String x, y
    If Len(a) = 0 Or Len(b) = 0 Then
        Return ""
    Elseif Right(a, 1) = Right(b, 1) Then
        LCS = LCS(Left(a, Len(a) - 1), Left(b, Len(b) - 1)) + Right(a, 1)
    Else
        x = LCS(a, Left(b, Len(b) - 1))
        y = LCS(Left(a, Len(a) - 1), b)
        If Len(x) > Len(y) Then Return x Else Return y
    End If
End Function

Print LCS("1234", "1224533324")
Print LCS("thisisatest", "testing123testing")
Sleep