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Instacart·Software Engineer·Online Assessment (OA)·Intermediate

IntermediateRejected
Jun 2026

Summary

Took the Instacart OA for a Software Engineer role and it did not go well. The main problem was an in-memory file system design question and I fumbled it pretty badly, finishing with a 450/600 which I doubt is enough to move forward.

Questions Asked (1)

Q1

Design and implement an in-memory file system that supports operations like adding files, copying files, matching files by prefix or suffix, and managing files per user.

System DesignAlgorithms & Data StructuresData Modeling
Author's notes

My brain just stopped working on the file vs.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then design a class-based in-memory file system with a trie for prefix matching and a reverse trie for suffix matching, and a map for user-to-files. Implement core operations like add, copy, and search, ensuring efficient time and space complexity.

Pro tip: Discuss trade-offs between different data structures (e.g., trie vs. hash map for prefix search) and mention how you would handle concurrent access or persistence if needed, showing awareness of real-world constraints.

1. Clarify Requirements

Ask questions to understand the scope: file content storage, user permissions, expected operations frequency, and whether files can be shared across users.

2. Design Data Structures

Propose using a trie for prefix matching, a reverse trie for suffix matching, and a hash map for user-to-files mapping. Consider storing file metadata and content separately.

3. Implement Core Operations

Outline methods for addFile, copyFile, findFilesByPrefix, findFilesBySuffix, and getUserFiles. Discuss time complexity for each.

4. Handle Edge Cases

Address duplicate file names, copying across users, empty prefixes/suffixes, and large numbers of files. Discuss memory management.

5. Optimize and Extend

Suggest optimizations like caching frequent searches, using a more space-efficient trie (e.g., compressed trie), and extending to support deletion or renaming.

Key Points to Mention

  • Trie data structure for efficient prefix matching
  • Reverse trie for suffix matching
  • Hash map for user-to-files mapping
  • Time complexity analysis for each operation
  • Handling of file content storage (e.g., in-memory strings or references)
  • Potential concurrency issues and solutions (e.g., locks or concurrent data structures)

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