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Openai·Software Engineer·Onsite - System Design / Architecture·Senior

Senior
Jun 2026

Summary

System design round at OpenAI for a software engineer role. The problem was a crossword puzzle system and I spent a good chunk of time just figuring out what they were even asking.

Questions Asked (1)

Q1

Design a system to solve crossword puzzles, considering both in-memory approaches and large-scale distributed processing.

System DesignAdaptability & AmbiguityTechnical Trade-offs
Author's notes

Spent way too long on clarifying questions at the start.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a baseline in-memory solution using backtracking with constraint propagation. Next, discuss scaling challenges and outline a distributed architecture that partitions the puzzle or dictionary, leveraging parallel search and caching. Finally, compare trade-offs between the two approaches and suggest a hybrid solution.

Pro tip: Emphasize that the core challenge is search space reduction, and show how techniques like constraint satisfaction and heuristics (e.g., letter frequency) can drastically improve performance before scaling out.

1. Clarify Requirements and Constraints

Ask about puzzle size, dictionary size, time limits, and whether the system needs to solve arbitrary puzzles or a specific format. This demonstrates adaptability and ensures you address the right problem.

2. Design In-Memory Solution

Propose a backtracking algorithm with constraint propagation (e.g., using AC-3) and heuristics like most-constrained-variable. Discuss data structures for efficient dictionary lookup (trie, DAWG).

3. Identify Scaling Bottlenecks

Analyze limitations of in-memory approach: memory for large dictionaries, single-machine compute limits, and inability to handle massive parallelism. This sets the stage for distributed processing.

4. Design Distributed Architecture

Outline a distributed system that partitions the search space (e.g., by puzzle regions or dictionary subsets) across workers, using a master-worker pattern with task queue and result aggregation. Mention fault tolerance and load balancing.

5. Compare and Recommend Hybrid Approach

Discuss trade-offs: in-memory is simpler and faster for small puzzles; distributed is necessary for large-scale or real-time solving. Suggest a hybrid where in-memory optimizations are used within each worker.

Key Points to Mention

  • Constraint satisfaction problem (CSP) formulation and backtracking with forward checking
  • Efficient dictionary representation (trie, DAWG) and word filtering
  • Parallelization strategies: task decomposition, MapReduce, or graph partitioning
  • Caching and memoization of partial solutions to avoid redundant work
  • Trade-offs between latency, throughput, cost, and complexity
  • Fault tolerance and dynamic scaling in distributed systems

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