I didn't understand why I should calculate the mean - the value. For me it would make more sense to calculate the value - mean, because if the value is 12 and the mean is 10 I would get 2 more. The way it's asked for here gives -2, when in fact, I collected 2 contacts more. What didn't I understand correctly? There is no way everyone did this wrong, without questioning.

It's the way noobs do it lol. Just like me haha :P

The description wasn't sufficient imo.
I did not understand, that I needed to set a default value, to pass the test cases.

I'm either 1 too high with half the test cases in one "solution" or 1 too low in half the cases in another, are the test cases alright??

Why is my code not working every time?

Well I solved that kata, but my while loop was so inefficient, that I got an execution time out for some tests and I could only pass the basic tests.