1- I was either careless about garbage filtering or instructions might have said not to worry about weird cases.Either way, I will be more careful it's good practice to handle those always.
2-3-Should assigning frequently used expressions such as n-1 or n-2 to a variable be better?(int firstPrecedingIndex=n-1;)
(I usually use Intellij to reformat the code and paste it back,but sometimes I have to use it because it interprets most of the faults unlike browser's editor).