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Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Bytedance coding round, one algorithmic question on interval gaps. Pretty straightforward problem on paper but the edge cases are where you can lose time.

Questions Asked (1)

Q1

Given a sorted array of unique integers and a lower and upper bound, return all missing ranges within [lower, upper] that are not covered by the array. Single-element gaps should be represented as just that element, multi-element gaps as a pair.

Algorithms & Data Structures
Author's notes

This is basically LC 228 but asking for the gaps instead of the covered ranges.

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AI HintsAI Generated

Suggested Approach

Use a linear scan through the sorted array while maintaining a pointer for the current expected number, starting at 'lower'. For each element, if it's greater than the current pointer, record the missing range from pointer to element-1; then update the pointer to element+1. After the loop, if the pointer is ≤ upper, record the final missing range.

Pro tip: Clarify edge cases upfront (e.g., empty array, bounds outside array range) and handle integer overflow by using long or careful arithmetic when computing element+1. Also, explicitly state the time and space complexity (O(n) time, O(1) extra space excluding output).

1. Understand the problem and edge cases

Restate the problem to ensure clarity: given a sorted unique array, find all missing ranges between lower and upper. Identify edge cases: empty array, array values outside bounds, single-element gaps, and multi-element gaps.

2. Initialize pointers and result list

Set a pointer 'prev' to lower (the start of the current missing range) and create an empty list for results. Iterate through each number in the array.

3. Process each array element

For each number 'num', if num > prev, then there is a missing range from prev to num-1. Add this range to the result (as a single number if prev == num-1, else as a pair). Then update prev to num+1.

4. Handle the final range after the loop

After processing all elements, if prev <= upper, add the missing range from prev to upper to the result.

5. Return the result and analyze complexity

Return the list of missing ranges. Explain that the algorithm runs in O(n) time and O(1) extra space (excluding the output list).

Key Points to Mention

  • Linear scan with a pointer to track the next expected number.
  • Handling of single-element gaps (output as a single integer) vs. multi-element gaps (output as a pair).
  • Edge cases: empty array, array values outside [lower, upper], and bounds equal to array elements.
  • Time complexity O(n) and space complexity O(1) extra space.
  • Avoiding integer overflow when computing num+1 or num-1, especially if bounds are near integer limits.
  • Clarifying the output format: list of ranges, where each range is either a single integer or a pair of integers.

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