Nextdoor·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Jul 2026Remote

Summary

Nextdoor software engineer interview with a meaty coding problem around version string comparison. The question had a lot of layers and I didn't fully anticipate how deep they'd want to go on the pre-release parsing piece.

Questions Asked (1)

Implement a compareVersions(a, b) function that compares two version strings with dot-separated numeric components, treating missing trailing parts as zero and ignoring leading zeros. Then extend it to handle optional pre-release tags like -alpha or -rc.1 (which sort before the release), compare pre-release tokens numerically or lexicographically depending on type, strip build metadata after '+', and return -1, 0, or 1. Also walk through complexity and describe edge case test coverage.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

Started fine with the basic numeric comparison, split on dots, parseInt to drop leading zeros, pad shorter arrays with zeros.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the version comparison rules and edge cases, then implement a step-by-step solution: first compare numeric components, then handle pre-release tags, and finally strip build metadata. Discuss time and space complexity, and outline a comprehensive test suite covering edge cases.

Pro tip: Mention that you would use a two-pointer approach to compare components without splitting the entire string, which is memory-efficient and handles large version strings gracefully. Also, explicitly state that you would write unit tests for each edge case to ensure robustness.

1. Clarify requirements and edge cases

Ask clarifying questions about version format, pre-release tag ordering, and build metadata handling. Identify edge cases like missing components, leading zeros, and empty strings.

2. Design the algorithm

Outline a plan: split version strings into numeric and pre-release parts, compare numeric components with zero-padding, then compare pre-release tags token by token, and finally ignore build metadata.

3. Implement the comparison logic

Write code to compare numeric components, handle pre-release tags (numeric vs lexicographic), and strip build metadata. Ensure the function returns -1, 0, or 1.

4. Analyze complexity and test coverage

Discuss time and space complexity (O(n) time, O(1) space with two-pointer). Describe test cases: equal versions, different lengths, leading zeros, pre-release tags, build metadata, and invalid inputs.

Key Points to Mention

Treat missing trailing numeric components as zero (e.g., 1.0 == 1.0.0).
Ignore leading zeros in numeric components (e.g., 1.01 == 1.1).
Pre-release tags sort before the release (e.g., 1.0-alpha < 1.0).
Compare pre-release tokens numerically if both are numeric, else lexicographically.
Strip build metadata after '+' and ignore it in comparison.
Time complexity O(n) and space O(1) with two-pointer approach; test edge cases like empty strings, multiple dots, and mixed types.

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