How to reclaim free space in big file

Hello team.

Excuse me if my question was resolved before, but I couldn't see a thread that have been solved for my question.

Let me explain it:

We have a big file for a tablespace in an ASM, for example:

The white space is free space, and the other colours is data from tables.

If we erase some tables, our big file could have an apparience like that:

If we do a resize, we could reclaim the free space until the HWM, so our big file look like that:

But our big file will be like a suize cheese.

So we could think to do a shrink in some tables: