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Dropbox·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Dropbox technical phone screen for a software engineer role, centered on a pretty gnarly adversarial word-guessing problem. The question had layers and pushed into algorithm design and pseudocode territory, which I wasn't fully warmed up for.

Questions Asked (1)

Q1

You have a word-guessing game where the word-selector is adversarial and can secretly swap the target word mid-game, as long as the new word stays consistent with all previously revealed hits and misses. How does the guesser minimize the worst-case number of guesses? Walk through your strategy and write pseudocode.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

This wrecked me a little.

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AI HintsAI Generated

Suggested Approach

Model the game as a minimax problem where the guesser selects guesses to minimize the maximum remaining candidate set size, and the adversary selects the response that maximizes it. Use a decision tree approach, choosing guesses that split the candidate set as evenly as possible, and provide pseudocode for the recursive minimax strategy.

Pro tip: Emphasize that the adversary's power is constrained by consistency with previous responses, so the guesser's optimal strategy is to maintain the set of all possible words and always guess a word that minimizes the worst-case remaining set size. This demonstrates understanding of game theory and algorithm design under adversarial conditions.

1. Formalize the problem

Define the game state as a set of possible target words consistent with all previous guesses and responses. The adversary can choose any word from this set and any response pattern that keeps at least one word consistent.

2. Define the minimax objective

The guesser wants to minimize the maximum number of guesses needed in the worst case. This is equivalent to minimizing the depth of the decision tree, where each node is a guess and edges are adversary responses.

3. Design the guessing strategy

At each step, for each possible guess (from the candidate set or a larger dictionary), compute the partition of the candidate set based on all possible response patterns. Choose the guess that minimizes the size of the largest partition.

4. Write pseudocode for the recursive minimax

Implement a function that takes the candidate set and returns the optimal guess and worst-case number of guesses. Use memoization to avoid recomputing states.

5. Analyze complexity and trade-offs

Discuss the computational cost of evaluating all guesses and partitions, and potential heuristics (e.g., limiting guesses to candidate set) for practical implementation.

Key Points to Mention

  • Minimax decision tree and worst-case optimality
  • Adversary's ability to swap words as long as consistent with hits/misses
  • Partitioning candidate set by response patterns (exact match, present but wrong position, absent)
  • Choosing guesses that minimize the maximum partition size (balanced splits)
  • Memoization and state representation for efficiency
  • Trade-off between optimality and computational feasibility; heuristics like guessing from candidate set

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