I love you

We can also modify global variable through IIB (Instance Initialization Blocks). You can check my solution for reference.

FYI error your code gives is:

Caused by: java.lang.IllegalArgumentException: count is negative: -1
	at java.base/java.lang.String.repeat(String.java:4412)`
	at Kata.towerBuilder(Kata.java:6)`

Looks like only way for that to happen is because your code does not handle nFloors of 0.

Apparently back then if I'm understanding correctly, the kata expected "int[]" to be returned instead of "HashMap<String, int>" despite saying that it needs to be an HashMap. So now, it's fixed but there's still backwards compatibility for "int[]" solutions.

Yeah, mine asked for a HashMap too. And we have the same solutions. I would say we are good. :)

the String u: find the digit at the end of str and plus 1 to it, else no change to string

return: check if the string has a digit -> then return it as is or plus 1

technically the return could be better written like this

return u==str?u+1:u;