Implement a Merkle Tree for Repository Diffing
Last updated: May 21, 2025
Quick Overview
Build a Merkle tree data structure that can efficiently diff two repository snapshots. Each leaf node represents a file hash, and internal nodes represent directory hashes. Implement tree construction and a diff function that identifies changed files without comparing every file.
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May 21, 20255
10
3,696 solved
Build a Merkle tree data structure that can efficiently diff two repository snapshots. Each leaf node represents a file hash, and internal nodes represent directory hashes. Implement tree construction and a diff function that identifies changed files without comparing every file.
Cursor needs to efficiently detect which files changed between two points in time to update its codebase index. A Merkle tree allows comparing entire directory subtrees with a single hash comparison, skipping unchanged subtrees entirely. This question tests your understanding of tree data structures and hashing.
What the Interviewer Expects
- Implement a Merkle tree with proper hash computation for files and directories
- Write a diff function that identifies changed files by comparing two trees
- Optimize traversal to skip unchanged subtrees
- Handle edge cases like file additions, deletions, and renames
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- How would you handle rename detection efficiently?
- What hash function would you choose and why?
- How would you extend this to support incremental tree updates?
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Practice DSA ProblemsSample Answer
Problem Analysis
To solve the problem of diffing two repository snapshots using a Merkle tree, we can identify that the problem requires a tree-based structure to efficiently compute and compare hashes for both files ...
Approach
The approach can be broken down into two main parts: constructing the Merkle tree and implementing the diff function.
- Merkle Tree Construction:
- For each directory, compute its hash by ha...
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