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Level: Mid-Level
Round: Phone Screen · Type: Coding · Difficulty: 7/10 · Duration: 75 min · Interviewer: Unfriendly
Topics: Data Structures, Algorithms, Memory Allocation
Location: San Francisco, CA
Interview date: 2026-01-19
I had a phone screen focused on data structures and algorithms. The question was about implementing a memory allocator.
The coding question I received was:
allocator(size=1000) malloc(size) -> pointer free(pointer) -> bool
The question was a memory allocator problem. Initially, I proposed a linked list solution with O(n) time complexity. The interviewer wasn't satisfied and asked me to brainstorm a better solution. I hadn't prepared for this specific problem, so I brainstormed on the spot and eventually came up with an O(log n) time complexity solution. My idea was to use a sorted list of free blocks (sorted by free size) combined with a linked list. The sorted list would be used to find a free block, and the linked list would handle bookkeeping.
I spent some time brainstorming, and then I spent time writing tests (I wrote a lot of tests, which might not have been necessary). Finally, the interviewer provided a few of their own tests, which all passed. The interview ended with just 5 minutes remaining. I'm not sure if this counts as completing the question.