Bloomberg Software Developer interview questions

I applied for an Industrial Placement in December and after one months they contacted me for a phone interview. The interviewer was a software engineer. He was very polite during the interview. After one week from the interview they asked me to do an interview on-site. I sent all what they needed to schedule the interview but after one day they wrote me that all positions for industrial placement 2017 were been filled. It was unprofessional, because they asked me just one day before to do the second interview.

telephonic interview 1 hour:-- what will you do if number is greater than current max size in the language - (use array to store the number) asked me to write a program with to add two integers store in an array format. (not that easy as it looks , took me whole 15 mins to write this...) we went over hashmap and hashset in java. why it is O(1) to for both. Also how hashcode gives location of element in the array in hashmap, what operation is performed to get it. and so on....