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Bytedance·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Apr 2026

Summary

Bytedance SWE interview that started with a classic string reversal problem and then took a sharp left turn into a variant I hadn't seen before. The follow-up about preserving exact spacing was the real test, and I don't think I handled the transition as smoothly as I should have.

Questions Asked (2)

Q1

Reverse the words in a string. Walk through your initial approach and any edge cases you'd test.

Algorithms & Data Structures
Author's notes

Split, reverse, join.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: whether to reverse the entire string or reverse the order of words while keeping characters within words intact. Then propose an efficient in-place algorithm using two-pointer swaps, and discuss edge cases like multiple spaces, leading/trailing spaces, and empty strings.

Pro tip: Mention that you can achieve O(1) extra space by reversing the entire string first, then reversing each word individually. This demonstrates strong algorithmic thinking and space optimization.

1. Clarify the problem

Ask whether 'reverse the words' means reversing the order of words (e.g., 'hello world' -> 'world hello') or reversing each word's characters. Also clarify handling of multiple spaces and punctuation.

2. Propose an approach

Suggest a two-step in-place algorithm: reverse the entire string, then reverse each word individually. This uses O(1) extra space and O(n) time.

3. Walk through an example

Demonstrate with a simple example like 'the sky is blue' to show how the algorithm works step by step.

4. Identify edge cases

List edge cases: empty string, single word, multiple spaces between words, leading/trailing spaces, and strings with only spaces.

5. Discuss testing and complexity

Explain how you would test the solution (unit tests for edge cases) and analyze time and space complexity (O(n) time, O(1) space).

Key Points to Mention

  • In-place reversal using two pointers to achieve O(1) extra space
  • Handling multiple consecutive spaces by skipping them during word reversal
  • Trimming leading and trailing spaces before processing
  • Time complexity O(n) and space complexity O(1)
  • Edge cases: empty string, single word, all spaces
  • Testing strategy: unit tests covering normal and edge cases

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

Q2

Now modify your solution so that the exact spacing from the input is preserved: leading spaces, trailing spaces, and the number of spaces between each word all stay the same. Only the word order reverses.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

This is where things got interesting and also where I fumbled a bit at first.

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AI HintsAI Generated

Suggested Approach

First, clarify that the problem now requires preserving the exact whitespace structure while reversing only the words. Then, propose a two-phase approach: tokenize the string into words and whitespace segments, reverse the order of words, and reassemble by interleaving the reversed words with the original whitespace segments in their original positions.

Pro tip: Mention that this approach avoids modifying the whitespace and handles edge cases like multiple spaces, leading/trailing spaces, and empty strings gracefully. Also, note that it runs in O(n) time and O(n) space, which is optimal for this problem.

1. Clarify requirements and edge cases

Confirm that only word order should change, and all whitespace (leading, trailing, between words) must remain exactly as in the input. Discuss edge cases: empty string, string with only spaces, multiple consecutive spaces, and single word.

2. Design tokenization strategy

Explain that you will parse the string into two lists: one for words (sequences of non-space characters) and one for whitespace segments (sequences of spaces). This separation allows independent manipulation.

3. Reverse word order

Reverse the list of words while keeping the whitespace segments list unchanged. This ensures the words are in reverse order but the whitespace structure remains intact.

4. Reassemble the string

Interleave the reversed words with the original whitespace segments in their original positions. If the string starts with whitespace, the first segment is whitespace; otherwise, it starts with a word. Continue alternating until all segments are used.

5. Analyze complexity and trade-offs

State that the time complexity is O(n) and space complexity is O(n) due to storing tokens. Mention that an in-place approach is complex due to varying whitespace lengths, so the token-based method is simpler and more maintainable.

Key Points to Mention

  • Tokenization into words and whitespace segments to preserve exact spacing.
  • Reversing only the word list, not the whitespace list.
  • Reassembly by interleaving reversed words with original whitespace segments.
  • Handling edge cases: leading/trailing spaces, multiple spaces, empty string.
  • Time and space complexity: O(n) time, O(n) space.
  • Trade-off: simplicity and correctness vs. potential in-place optimization.

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