The interview process involved two rounds, both conducted on the university campus.

It was a nice experience; the interviewers were patient and encouraging.

They are looking for a candidate who is very comfortable with basic data structures and their operations.

Given a string, sort its letters by frequency and in alphabetic order in the case of a tie. For example: BLOOMBERG -> BBOOEGLMR.

You have a million people running a marathon. The progress of the race is tracked via a series of check-points, A through Z. Describe two functions:

1. The first returns a list of 10 leaders in the race.
2. The second is called each time a person crosses a checkpoint and maintains a data structure for the proper functioning of the first function.

How would you implement a cache for storing large amounts of frequently updated data? What would be the time performance of insert, remove, and search?