Evil Hangman (Adaptive Secret Word) — Minimum Guesses to Guarantee a Win
Question Details
You are given a set of candidate words for a Hangman-like game, but the opponent can adaptively change the secret word after each guess as long as it remains consistent with the current board stat
Full Details
You are given a set of candidate words for a Hangman-like game, but the opponent can adaptively change the secret word after each guess as long as it remains consistent with the current board state. Compute, in the worst case, the minimum number of letter guesses needed to guarantee identifying the answer.
Rules
- Initially the opponent chooses a secret word from
words, but after each guessed letter they may switch it to any other word still consistent with the revealed board. - The board shows:
- revealed letters in their exact positions
_for unknown positions- Each guess is a single letter (a-z).
- The opponent tries to maximize how long you cannot pin down a unique word; you try to minimize the worst-case number of guesses needed to force the candidate set to a single word.
Input
- words: a non-empty array of lowercase words
- all words have the same length
Output
- An integer: the minimum number of guesses required (under optimal play) to guarantee the remaining candidate set becomes a singleton.
Constraints
- 1 <= len(words) <= 2000
- 1 <= word_length <= 20
- 26 lowercase letters; assume each letter can be guessed at most once (you may enforce this).
Implement
min_guesses_to_guarantee(words: List[str]) -> int
Provide a time complexity analysis.
Sample Input
["ally","beta","cool","deal"]
Sample Output
(implementation-dependent; verify by running your algorithm)
Test Cases
Case 1
Input:
["ally","beta","cool","deal"]
Output:
(implementation-dependent; verify by running your algorithm)
Case 2
Input:
["aa","ab","ba","bb"]
Output:
(implementation-dependent; verify by running your algorithm)
Case 3
Input:
["abc"]
Output:
0
Case 4
Input:
["aaaa","aaab","aaba","abaa","baaa"]
Output:
(implementation-dependent; verify by running your algorithm)
Case 5
Input:
["abcd","abce","abde","acde","bcde"]
Output:
(implementation-dependent; verify by running your algorithm)
About This Question
This is a reported interview question from a dropbox interview for a swe role during the coding round.
It covers the following topics: Arrays .
Topics
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About Dropbox Interview Reports
This question was reported by a candidate who interviewed at Dropbox. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Dropbox are the higher-signal extractions to take from this report.
For broader preparation context, the Dropbox interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Dropbox reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Dropbox Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Dropbox reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.