done.

omg.
I sat for two hours calculating algebraic formulas. And here everything was so simple

My brain has yet to reach this level of logic building.

which language ?

kata retired.

thats what comments are for.

Fixed.

...I don't think it's good practice to modify the parameters you were given without being told to, especially if the original function signature marks the array with const.

It's a variable template. In this particular case, making it not a function probably forces more creative solutions

Be careful with random tests for the final attempt, in my case sometimes they worked and sometimes not.
It should be better to have fixed tests that can be passed only by respecting certain conditions.

The description should clarify that:

• the id column is unique (reading the description, I first thought I had to GROUP BY id to collect the first and last ip each user connected from. This would make sense for a database that logs a triplet (user_id, user_ip, connection_time) each time a user connects to a server, as the description alludes to)
• the ip_address column is not a simple address, it is an address with a submask (denoted by a / character in the textual representation)

done