System failure troubleshooting: You can only SSH into the machine and the log file is huge. How would you locate the problem quickly?
Flip a bit: Given an integer num and a bit position, flip that bit.
Concurrency bug: Given multithreaded code that uses locks, find and fix the deadlock.
Word frequency top-K: Given a directory that may contain nested sub-directories and files, count word frequencies across all files and return the top-K words. Follow-ups: handle too many files to fit in memory (MapReduce vs Count-Min Sketch + Space-Saving).