Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Bytedance software engineer screen with a range-finding array problem. Pretty standard coding round but the edge case handling tripped me up more than I expected.

Questions Asked (1)

Given a sorted array of distinct integers and a lower and upper bound, return all maximal ranges within that interval that are missing from the array. Represent single missing values as a one-element range and consecutive gaps as a start-end pair.

Algorithms & Data Structures

Author's notes

I spent too long overthinking the representation format and not enough time on the actual traversal logic.

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AI HintsAI Generated

Suggested Approach

Treat the problem as finding gaps between consecutive elements in the sorted array, including the boundaries. Iterate through the array while maintaining the current lower bound, and for each element, if there's a gap between the current bound and the element, add the missing range. After processing all elements, check for a gap between the last element and the upper bound.

Pro tip: Clarify edge cases upfront, such as when the array is empty, when all numbers are outside the bounds, or when the bounds themselves are missing. This shows attention to detail and prevents incorrect assumptions.

1. Understand the problem and edge cases

Restate the problem to ensure clarity: we need all maximal ranges of missing integers within [lower, upper]. Discuss edge cases like empty array, no missing numbers, or bounds outside the array's range.

2. Initialize and iterate

Set a variable `prev` to `lower - 1` (or `lower` and handle separately). Iterate through each number in the sorted array, and for each, check if there's a gap between `prev` and the current number.

3. Identify and add missing ranges

If `prev + 1 < current`, then the missing range is from `prev + 1` to `current - 1`. Add this range to the result, formatting as a single number if start equals end, otherwise as 'start->end'.

4. Handle the final gap

After the loop, check if `prev < upper`. If so, add the range from `prev + 1` to `upper`.

5. Return the result

Return the list of missing ranges. Ensure the output format matches the problem's requirement (e.g., strings like 'a->b' or single numbers).

Key Points to Mention

Time complexity: O(n) where n is the length of the array, as we traverse the array once.
Space complexity: O(1) extra space excluding the output list.
Handling of boundaries: ensure lower and upper are inclusive and properly checked.
Formatting of ranges: single missing values as one-element ranges, consecutive as start->end.
Edge cases: empty array, no missing numbers, array elements outside bounds.
Use of a sentinel or previous pointer to track the last seen number.

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