Seems that the internal implementation details is complex comparative to using a buffer - especially in terms of code conciseness. Just an opinion tho.

Thats nice.
This didnt divide number, but check if last bit of it is one.
So must work faster and require less resources.

LOL! It look like cheat =))

It's hardtyped PHP this is rather usefull but not requird by PHP.

Your right, the best solution is sort and then find duplicates

Thats readable but not very performatic!

It looks through the entire data set though, when the solution might be obvious after 3 reads. The original brief did state "The tests contain some very huge arrays, so think about performance.".

if len(arr) == 0 then arr[0] will panic

I find this idiomatic, understandable and clever. Should be on top of best practices.

The source code of strings.Repeat implementation should be the clever answer to this kata.

I had to test, did not think this would work for the value 0 - it does