Problem with code

why in line 15 , -1 is done even after defining compare. also plz explain what does a and b denote inside compare function

I hope I’ve cleared your doubt. I ask you to please rate your experience here
Your feedback is very important. It helps us improve our platform and hence provide you
the learning experience you deserve.

On the off chance, you still have some questions or not find the answers satisfactory, you may reopen
the doubt.