Hot Agent Startup·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Technical phone screen at a hot agent startup for a software engineer role. One algorithmic question, pretty focused, felt like they were testing how carefully you think through edge cases rather than just whether you can code.

Questions Asked (1)

Given a sorted list of time-series readings (each with a timestamp and intensity value) and a threshold, return all maximal time intervals where the intensity strictly exceeds the threshold. Readings model a step function, and you're given an observation end time to cap the final interval. Return half-open intervals. Be prepared to discuss edge cases like empty input, duplicate timestamps, unsorted input, and whether the threshold boundary is inclusive or exclusive.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I got the basic scan working pretty fast but then they started poking at edge cases and I started second-guessing myself.

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AI HintsAI Generated

Suggested Approach

Start by clarifying assumptions and edge cases, then propose a single-pass O(n) algorithm that scans readings while tracking whether intensity is above threshold. Emphasize the step-function semantics and half-open interval output, and discuss trade-offs like handling unsorted input or duplicate timestamps.

Pro tip: Explicitly state that the threshold is strict (>), so intervals are half-open and boundary points are excluded; this avoids ambiguity and shows attention to detail. Also, mention that you would confirm whether the input is guaranteed sorted or if you need to sort it first, as that affects complexity.

1. Clarify requirements and edge cases

Ask about input guarantees (sorted, duplicates, empty), threshold inclusivity, and output format (half-open intervals). Confirm the observation end time caps the final interval.

2. Define the algorithm

Propose a single-pass scan: iterate through readings, track the start of an above-threshold interval when intensity first exceeds threshold, and close the interval when intensity drops to or below threshold or at the end time.

3. Handle edge cases

Address empty input, all values below/above threshold, duplicate timestamps (decide on tie-breaking), unsorted input (sort first or assume sorted), and the final interval capping at observation end time.

4. Analyze complexity and trade-offs

State time and space complexity (O(n) time, O(1) extra space if sorted; O(n log n) if sorting needed). Discuss trade-offs between assuming sorted input vs. sorting, and handling duplicates.

5. Test with examples

Walk through a small example, including boundary cases (intensity exactly equal to threshold) to verify the half-open interval logic and edge case handling.

Key Points to Mention

Threshold is strict (>), so intervals are half-open and exclude points where intensity equals threshold.
Step-function semantics: intensity changes only at timestamps, so intervals are defined by consecutive readings.
Edge cases: empty input, duplicate timestamps, unsorted input, all values above/below threshold, and final interval capping at observation end time.
Algorithm: single pass with state tracking, O(n) time if sorted, O(1) extra space.
Trade-offs: sorting unsorted input adds O(n log n) time; duplicate timestamps require a tie-breaking rule (e.g., last value wins).
Output format: list of half-open intervals [start, end) where intensity > threshold.

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