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Decagon interview notes, page 4 of 4

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Most of these Decagon write-ups come from Software Engineers (30), then AI Engineers (1). The most reported rounds are the technical phone screen (22), the system design round (8) and the behavioral / leadership round (1).

31 interview notes · updated Jul 2026

Decagon·Software Engineer·Technical Phone Screen

Jul 2026
Decagon software engineer interview with a system design coding problem centered on a sliding window data structure. The follow-up pushed into update semantics which is where things got more interesting.
  • Design a class with an insert method and a get_avg method, where get_avg returns the average of all values whose timestamps fall within a fixed time window ending at the given timestamp. Timestamps are guaranteed to be non-decreasing across calls.
  • Follow-up: add an update method that can modify the value or refresh the timestamp of an existing record by its ID. What data structures would you need, and what are the tradeoffs between O(log n) and O(1) update complexity?

“The monotonic timestamp constraint is the key thing to notice early.”

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