I am following a [previous post](https://stackoverflow.com/questions/47752/remove-duplicates-from-a-listt-in-c) on stackoverflow about removing duplicates from a `List<T>` in C#.

If `<T>` is some user defined type like:

```
class Contact
{
    public string firstname;
    public string lastname;
    public string phonenum;
}

```

The suggested (HashMap) doesn't remove duplicate. I think, I have to redefine some method for comparing two objects, isn't it?