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Openai·Software Engineer·Technical Phone Screen·Senior

SeniorPass
May 2026Remote

Summary

OpenAI phone screen for a software engineer role. Five questions total, got through three cleanly, stumbled on the fourth, never even saw the fifth. Moved forward anyway, which was a relief.

Questions Asked (3)

Q1

Solve the 'Infected Plants' problem and its sub-questions (five parts total).

Algorithms & Data Structures
Author's notes

Got through the first three parts fine.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem statement and constraints for each sub-question, as the 'Infected Plants' problem likely involves grid-based infection spread with variations. Then, for each part, identify the appropriate algorithm (e.g., BFS/DFS for simulation, binary search for optimization, or mathematical modeling) and discuss time/space complexity. Finally, code a clean solution and test with edge cases.

Pro tip: Demonstrate strong communication by restating the problem in your own words and asking targeted questions about constraints (e.g., grid size, infection rate, multiple sources) before diving into solutions. This shows you prioritize understanding over rushing to code.

1. Clarify the problem and constraints

Ask questions to understand the exact rules of infection spread, grid dimensions, input format, and what each sub-question asks. Confirm assumptions about time steps, infection conditions, and output requirements.

2. Identify the core algorithm for each part

For simulation-based parts, consider BFS/DFS or multi-source BFS. For optimization parts (e.g., minimum time, maximum spread), consider binary search on time or dynamic programming. For counting or probability parts, use combinatorics or DP.

3. Analyze complexity and trade-offs

For each approach, state time and space complexity. Discuss trade-offs between different algorithms (e.g., BFS vs. union-find for connectivity) and choose the most efficient for the given constraints.

4. Implement and test

Write clean, modular code for each sub-question, handling edge cases like empty grid, no infection, or all infected. Test with small examples and trace through to verify correctness.

5. Review and optimize

After implementing, review for potential optimizations (e.g., early termination, pruning) and ensure the solution scales. Discuss how you would handle larger inputs or additional constraints.

Key Points to Mention

  • Multi-source BFS for simulating infection spread from multiple initial infected plants.
  • Binary search on answer for problems like 'minimum time to infect all plants'.
  • Dynamic programming for counting infection sequences or probabilities.
  • Union-Find (Disjoint Set Union) for connectivity problems if infection spreads through connected components.
  • Time and space complexity analysis for each sub-question.
  • Edge cases: empty grid, no initial infection, all plants infected, obstacles, and varying infection rates.

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

Q2

Design a solution that solves a crossboard traversal problem as part of the infected plants series.

Algorithms & Data StructuresSystem Design
Author's notes

This was embedded inside the larger problem set.

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AI HintsAI Generated

Suggested Approach

Clarify the problem by defining the grid, infection spread rules, and traversal constraints, then propose an algorithm (e.g., BFS/DFS) to traverse the grid and compute the required outcome. Discuss trade-offs between different approaches and consider scalability for large grids.

Pro tip: Demonstrate awareness of edge cases like multiple sources, obstacles, and infinite loops, and mention how you would test and optimize the solution for performance.

1. Clarify the Problem

Ask questions to understand the grid dimensions, infection spread rules (e.g., 4-directional, time steps), and what exactly needs to be computed (e.g., time to infect all, number of steps).

2. Choose an Algorithm

Select an appropriate traversal algorithm such as BFS for shortest path or DFS for connectivity, and justify your choice based on the problem requirements.

3. Design the Solution

Outline the steps: initialize data structures (queue, visited set), process initial infected cells, iterate until all reachable cells are infected or queue is empty, and track time/steps.

4. Analyze Complexity

Discuss time and space complexity (e.g., O(m*n) for BFS) and consider optimizations for large grids or multiple queries.

5. Handle Edge Cases

Address scenarios like no initial infected cells, unreachable cells, and multiple infection sources, and explain how your solution handles them.

Key Points to Mention

  • BFS for level-by-level traversal to simulate infection spread over time
  • Use of a queue to process cells in order of infection time
  • Tracking visited cells to avoid reprocessing and infinite loops
  • Time and space complexity analysis (O(m*n) time, O(m*n) space)
  • Handling multiple sources by initializing the queue with all infected cells
  • Edge cases: empty grid, no spread possible, all cells infected initially

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

Q3

Design a distributed DFS system. How would you handle fault tolerance, early termination, constraint propagation, and deciding when to split work across nodes versus running DFS locally?

System DesignTechnical Trade-offsAlgorithms & Data Structures
Author's notes

This is the one that really got me.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem scope and constraints, then propose a master-worker architecture with dynamic work stealing and checkpointing. Discuss trade-offs between parallelism and overhead, and explain how to handle fault tolerance, early termination, and constraint propagation.

Pro tip: Emphasize that the decision to split work should be based on a cost model that considers the size of the search space, communication overhead, and load balancing; avoid splitting too aggressively as it can lead to diminishing returns.

1. Clarify Requirements and Constraints

Ask about the graph size, density, expected depth, available resources, and latency requirements to tailor the design.

2. Propose a Distributed Architecture

Outline a master-worker model where the master maintains a work queue of subtrees and workers request work, with a distributed hash table or shared storage for visited nodes.

3. Address Fault Tolerance and Early Termination

Use heartbeat mechanisms and checkpointing for fault tolerance; for early termination, implement a global termination detection algorithm like Dijkstra's or a token-based scheme.

4. Handle Constraint Propagation and Work Splitting

Propagate constraints by sharing discovered bounds or pruned branches; decide to split work when the subtree size exceeds a threshold and communication overhead is justified.

5. Discuss Trade-offs and Optimizations

Compare static vs dynamic partitioning, synchronous vs asynchronous communication, and suggest optimizations like work stealing and adaptive thresholds.

Key Points to Mention

  • Master-worker architecture with dynamic load balancing
  • Fault tolerance via checkpointing, replication, and heartbeat
  • Early termination using global termination detection algorithms
  • Constraint propagation through shared bounds and pruning
  • Cost model for splitting work: subtree size vs communication overhead
  • Work stealing to handle load imbalance and improve utilization

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