If you are going to support Kotlin in Leetcode, could you at least do a search and replace for using the keyword val as a variable name? Rather than surrounding it with the weird apostrophes? Replace it with value or target or something.

Secondly, If you are going to suggest using null in the answer if the solution requires a placeholder, could you at least make the 'answer' collestion nullable?

Also it's great fun when you're given an IntArray and told to use "-" in it as an empty cell value. I don't think it would take much to say something like use -1 as a empty cell value and then I'm not left wondering if the judging code is going to work or not. It's like: Should I use 0? Should I use -1? Should I use NaN?