sierra·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Sierra SWE interview with a coding problem around chunking markdown files. Pretty niche problem, not your typical leetcode grind, but the edge cases were where it got interesting.

Questions Asked (1)

Given a markdown file, split it into chunks that each respect a maximum size limit. When a chunk boundary cuts into content that falls under one or more headers, the new chunk must start by repeating those ancestor headers before the content.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The base chunking part felt manageable but the header-prepending requirement is where I started second-guessing myself.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: max chunk size, whether to split on semantic boundaries (e.g., paragraphs, code blocks), and how to handle oversized atomic blocks. Then outline a two-pass algorithm: first parse the markdown into a hierarchical structure tracking headers, then greedily pack blocks into chunks while maintaining a stack of ancestor headers to prepend when a new chunk starts.

Pro tip: Mention that you'd treat headers as a stack and only include the minimal set of ancestors needed for context, avoiding redundant repetition of headers that are already at the top of the chunk. Also, discuss the trade-off between strict size limits and semantic coherence—sometimes exceeding the limit slightly is better than splitting a code block.

1. Clarify requirements and edge cases

Ask about the maximum size unit (characters, bytes, tokens), whether chunks should be split at semantic boundaries, and how to handle content that exceeds the limit on its own (e.g., a large code block).

2. Parse markdown into a hierarchical block structure

Use a markdown parser to tokenize the document into blocks (headings, paragraphs, lists, code blocks) and build a tree or flat list with header levels and ancestor relationships.

3. Greedily pack blocks into chunks with header context

Iterate through blocks, maintaining a stack of current headers. When adding a block would exceed the limit, start a new chunk: prepend the current header stack (as markdown) before the block, then reset the stack to those headers.

4. Handle oversized atomic blocks and boundary cases

If a single block exceeds the limit, decide whether to split it (e.g., by lines) or allow it to exceed; if splitting, ensure headers are repeated in each sub-chunk. Also handle documents with no headers or nested headers correctly.

5. Validate and discuss trade-offs

Test with edge cases (deeply nested headers, large code blocks, empty sections). Discuss trade-offs: strict size vs. semantic coherence, performance of parsing vs. streaming, and whether to include header hierarchy in metadata instead of repeating.

Key Points to Mention

Use a stack to track the current header hierarchy and only repeat the minimal ancestor headers needed for context.
Split at semantic boundaries (e.g., between blocks) rather than arbitrary character positions to preserve readability.
Handle oversized atomic blocks (like code blocks) by either allowing them to exceed the limit or splitting them with repeated headers.
Consider performance: parsing the entire document upfront vs. streaming, and the cost of repeated header insertion.
Discuss trade-offs between strict adherence to max size and maintaining semantic coherence.
Mention edge cases: documents with no headers, deeply nested headers, and headers that are themselves longer than the limit.

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