round 1: behavioral questions + coding
Behavioral questions: a time you made a decision with incomplete information; a time you disagreed with a teammate or your manager and how you handled it
Coding: Given an array of strings, group together all words that are anagrams of each other and return the groups. The interviewer also asked me not to use the O(n·k log k) approach with sorted signatures.
Approach: Use a length-26 count signature as the map key (the counts can also be encoded as an integer), group the words in one pass, and collect all the values at the end. After writing it, I ran a few cases and discussed the pitfalls of using a product of primes as the key: overflow and collisions.
round 2: coding + behavioral questions
Behavioral questions: a time you took ownership of something clearly outside your scope; a time something you owned went wrong in production
Coding 1: Given a nonempty integer array, return the k most frequent elements.
Coding 2: Given a two-dimensional matrix containing only 0s and 1s, return the number of islands (1s connected up, down, left, or right). The follow-up asked for the largest island's area.
Follow-up 1: What if the matrix comes in as a stream, one row at a time?
round 3: coding + behavioral questions
Behavioral questions: Around Operational Excellence and Cost: whether I'd actually been on call, my first reaction to a production alert, whether I'd taken the initiative to reduce costs or improve performance, and whether complexity I'd introduced had ever come back to bite me.
Coding: An open-ended in-memory cache question.
Approach: Clarification should at least cover whether the capacity limit or TTL takes priority, lazy expiration versus active cleanup, the eviction policy (LRU/LFU), and whether concurrent reads and writes need locking. By the end of the discussion, we settled on an LRU cache with TTL. The follow-up asked how to replace the scheduled task that scans the whole table by time to find expired keys.
round 4: Bar Raiser
This round was almost entirely behavioral. The interviewer picked two or three experiences and kept digging: what happened, what I personally did, why that decision, and the measurable outcome, going deeper into the details each time. Many questions drilled down into specific numbers and exactly what my own contribution was.
- Taking a calculated risk: Describe something I knew was risky but pushed forward anyway. How did I quantify the risk, what was the fallback plan, how did it turn out, and would I change anything if I did it again?
- Influencing without authority: How did I get others to cooperate without a reporting relationship? What specific methods did I use, how many times was I turned down, and how did I get it done in the end?
They left a big chunk of time at the end for my questions. Prepare them beforehand instead of thinking them up on the spot.
Discussion
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