Can't figure out how to approach find_loop_start()

I’m stuck here for quite a bit, and am not able to understand how I can find out the start point of the loop.

I would suggest go through this link once
Also, there are plenty of articles out there regarding this. You can read the algorithms and try to implement it

Closing this topic as your issue is resolved by the mentor. If it is still not resolved, Kindly un-mark the accepted solution or create a new topic and post this question as a reference link in the description of the new topic.