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Openai·Software Engineer·Technical Phone Screen·Senior

Senior
May 2026

Summary

Interviewed for a software engineering role at OpenAI and got hit with a pretty gnarly algorithmic problem that built on a grid simulation. The core challenge was around optimal burn decisions to minimize plant deaths, and the discussion went deep into state space complexity and whether any exact polynomial solution even exists.

Questions Asked (1)

Q1

You have a grid simulation where plants can infect, recover, or die each day. At the start of any day, you can burn an entire row or column, removing all plants on it permanently. Design an algorithm to minimize the total number of plant deaths across the full simulation and return that minimum count.

Algorithms & Data StructuresTechnical Trade-offsSystem Design
Author's notes

This one took me a minute to even parse.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and simulation rules first, then model it as an optimization problem where burning rows/columns is a decision that affects future infections. Propose a dynamic programming or greedy approach with state representing burned rows/columns and current infected set, and analyze time complexity.

Pro tip: Discuss trade-offs between exact optimality and computational feasibility; for large grids, suggest heuristic or approximation algorithms and explain why exact solution is NP-hard.

1. Clarify Problem Details

Ask about grid size, infection/recovery/death probabilities, whether burns are permanent, and if multiple burns can be done per day. Confirm the objective: minimize total deaths over entire simulation.

2. Model as State-Space Search

Represent the state as (day, burned rows, burned columns, infected cells). Each day, choose to burn a row/column or do nothing, then simulate infections/recoveries/deaths. Use BFS/DFS with memoization to find optimal sequence.

3. Optimize with Dynamic Programming

If grid is small, use DP over subsets of rows/columns burned. For larger grids, note that the problem is likely NP-hard and propose a greedy heuristic: burn rows/columns with highest current infection count.

4. Analyze Complexity and Trade-offs

Discuss time/space complexity of exact DP (exponential in rows+columns) versus greedy (polynomial). Suggest approximation guarantees or Monte Carlo simulation for stochastic elements.

5. Test and Validate

Walk through a small example to verify the algorithm, and consider edge cases like all plants infected initially, no infections, or burning all rows/columns.

Key Points to Mention

  • State representation and transition function for daily simulation
  • Dynamic programming with bitmask for burned rows/columns
  • NP-hardness and need for heuristics on large grids
  • Greedy strategy: burn row/column with maximum infected plants
  • Trade-off between exact optimality and computational efficiency
  • Handling stochasticity via expected values or Monte Carlo

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