Dropbox·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Dropbox software engineer interview with a coding round built around implementing the core feedback logic for a Wordle-style game. Pretty clean problem once you break it down, but the misplaced match counting tripped me up at first.

Questions Asked (1)

Implement the feedback function for a word-guessing game: given a dictionary of valid words, a secret word, and a player's guess, return the number of exact position matches and the number of misplaced (right letter, wrong position) matches. Invalid guesses should be signaled clearly.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The exact match part is straightforward, just zip the two strings and count.

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AI HintsAI Generated

Suggested Approach

First, clarify requirements and edge cases, such as invalid guess handling and duplicate letters. Then, describe a two-pass algorithm: first count exact matches, then count misplaced matches using frequency counts of remaining letters. Finally, discuss trade-offs and potential optimizations.

Pro tip: Mention that the two-pass approach with frequency counting correctly handles duplicate letters, which is a common pitfall. Also, explicitly state how you would signal invalid guesses, e.g., by throwing an exception or returning a sentinel value, and justify your choice.

1. Clarify requirements and edge cases

Ask about input validation, handling of duplicate letters, and expected output format for invalid guesses. Confirm whether the guess must be in the dictionary and whether the secret word is always valid.

2. Design the algorithm

Outline a two-pass approach: first count exact matches and mark those positions as used. Then, for remaining positions, count letter frequencies in the secret and guess to determine misplaced matches.

3. Handle invalid guesses

Decide on a clear signaling mechanism, such as throwing an exception or returning a special value (e.g., -1 for both counts). Explain your choice based on the context.

4. Analyze complexity and trade-offs

State that the algorithm runs in O(n) time and O(1) space (since alphabet size is constant). Discuss alternative approaches, like using a hash map, and their trade-offs.

5. Test with examples

Walk through test cases, including duplicates (e.g., secret 'APPLE', guess 'PAPER') and invalid guesses, to verify correctness.

Key Points to Mention

Two-pass algorithm: first exact matches, then misplaced matches using frequency counts.
Handling duplicate letters correctly by decrementing counts after exact matches.
Invalid guess handling: throw an exception or return a sentinel value, with justification.
Time and space complexity: O(n) time, O(1) space (constant alphabet size).
Edge cases: empty strings, guesses not in dictionary, secret word with repeated letters.
Potential optimizations or alternative approaches, such as using a hash map for frequency counting.

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