Verkada Inc.·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Interviewed at Verkada for a software engineer role and got a time series problem that looked clean on the surface but had a bunch of edge cases hiding underneath. The clarification phase was basically the whole challenge.

Questions Asked (1)

You're given a time series from a surveillance camera as a list of (timestamp, value) pairs with strictly increasing timestamps. Given a threshold T, find and return all maximal contiguous intervals where the value exceeds T.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The problem sounds like a basic scan until you actually think about what 'interval' means for irregular samples.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose a single-pass linear scan that tracks the start of the current interval when the value exceeds T and closes it when the value drops to or below T. Discuss time and space complexity, and consider follow-up questions about streaming data or large inputs.

Pro tip: Mention that the timestamps are strictly increasing, so you can rely on the input order and avoid sorting; also, explicitly handle the case where the interval extends to the end of the series.

1. Clarify requirements and edge cases

Ask about the definition of 'exceeds' (strictly greater than T?), whether intervals are inclusive of endpoints, and how to handle empty input or no intervals. Confirm the output format (e.g., list of (start_timestamp, end_timestamp) pairs).

2. Outline the algorithm

Propose a single-pass approach: iterate through the list, and when value > T, mark the start if not already in an interval; when value <= T, close the interval if one is open. At the end, close any open interval.

3. Analyze complexity and trade-offs

State that the algorithm runs in O(n) time and O(1) extra space (excluding output). Discuss potential alternatives like binary search if the data were sorted by value, but note that timestamps are the key ordering.

4. Handle edge cases and test

Walk through examples: all values above T, none above T, alternating, and interval at the end. Ensure the code correctly handles these without off-by-one errors.

5. Discuss extensions and real-world considerations

Mention how to adapt for streaming data (e.g., maintaining state), memory constraints, or if the data is too large to fit in memory. Relate to surveillance camera use case (e.g., detecting motion events).

Key Points to Mention

Strictly increasing timestamps allow a single pass without sorting.
Definition of 'exceeds' as strictly greater than T.
Handling of intervals that start at the first element or end at the last element.
Time complexity O(n) and space complexity O(1) for the scan.
Output format: list of (start_timestamp, end_timestamp) pairs.
Potential follow-up: how to handle streaming data or very large inputs.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.