Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Bytedance SWE interview, got a classic interval problem that looks straightforward until you're actually coding it under pressure. Nothing too exotic but the details matter.

Questions Asked (1)

Given a sorted list of non-overlapping intervals and a new interval, insert the new interval and merge any overlaps. Return the result sorted and non-overlapping.

Algorithms & Data Structures

Author's notes

I knew the general shape of the solution pretty fast: walk through the list, dump everything that ends before the new interval starts, then keep merging anything that overlaps by stretching the new interval's bounds, then tack on the rest.

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AI HintsAI Generated

Suggested Approach

Use a linear scan to process intervals in three phases: add all intervals that end before the new interval starts, merge all overlapping intervals with the new interval, then add the remaining intervals. This achieves O(n) time and O(n) space, which is optimal since the input is already sorted.

Pro tip: Clarify edge cases upfront: empty input, new interval before all, after all, or overlapping multiple intervals. Also mention that if the input weren't sorted, you'd need to sort first (O(n log n)), but since it's sorted, linear is optimal.

1. Clarify and confirm assumptions

Ask if intervals are inclusive/exclusive, if the list can be empty, and if the new interval is guaranteed to be valid. Confirm that the result should be a new list or modified in-place.

2. Outline the three-phase linear approach

Explain that you'll iterate through intervals: first add those ending before the new interval starts, then merge overlapping ones by updating the new interval's bounds, and finally add the rest.

3. Walk through an example

Trace a concrete example (e.g., intervals = [[1,3],[6,9]], new = [2,5]) to demonstrate how the phases work and how merging updates the start and end.

4. Analyze complexity and edge cases

State time O(n) and space O(n) for the output. Discuss edge cases: new interval before all, after all, overlapping multiple, or empty input.

5. Write clean code

Implement with a single loop and clear conditions. Use a result list and append intervals as you go, avoiding unnecessary nested loops.

Key Points to Mention

Linear scan with three phases: before, merge, after
Time complexity O(n) and space O(n) due to sorted input
Merging condition: intervals overlap if interval.start <= newInterval.end and interval.end >= newInterval.start
Edge cases: empty list, new interval before first, after last, overlapping multiple
In-place modification vs creating new list (clarify with interviewer)
If input unsorted, sort first (O(n log n)) but not needed here

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