Design Tic-Tac-Toe
A medium-tier problem at 59% community acceptance, tagged with Array, Hash Table, Design. Reported in interviews at Chewy and 12 others.
Design Tic-Tac-Toe is a medium-difficulty system design problem that has appeared at Airbnb, Tesla, Shopify, Atlassian, and nine other major companies. You're asked to build a class that manages the game state, validates moves, and detects wins. Acceptance rate sits at 59 percent, which sounds reasonable until you hit the live assessment and realize the trick isn't obvious. The problem looks deceptively simple because tic-tac-toe itself is simple. The real challenge is building a clean, extensible interface that doesn't hardcode the win condition. StealthCoder surfaces a working solution in seconds if you blank on the state-management pattern during your OA.
Companies that ask "Design Tic-Tac-Toe"
Design Tic-Tac-Toe is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderMost candidates start by hardcoding a 3x3 matrix and checking all eight win lines after every move. That works but scales poorly and feels fragile. The pattern that matters is tracking moves per player (typically via Hash Table or Array) and validating wins efficiently without redundant checks. Some interviewers ask you to support variable board sizes, others want you to optimize for repeated queries. The common pitfall is over-engineering state tracking or writing brittle win-detection logic that only works for 3x3. Another trap: not thinking through whose turn it is, or handling invalid moves sloppily. Design problems reward clarity and intentionality. If your OA requires you to explain your choices and you haven't rehearsed the tradeoffs between a matrix and a hash-based state, you'll stumble. StealthCoder bridges that gap during the assessment itself.
Pattern tags
You know the problem.
Make sure you actually pass it.
Design Tic-Tac-Toe recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Design Tic-Tac-Toe interview FAQ
Is Design Tic-Tac-Toe actually asked at FAANG?+
Yes. It's been reported at Airbnb, Tesla, Shopify, and Atlassian, among others. It's not as frequent as LeetCode-style algorithm problems, but it shows up in system design or object-oriented design rounds. The 59 percent acceptance rate suggests it's not trivial.
What's the actual trick to this problem?+
Most people hardcode 3x3 boards and loop through eight win lines. The real pattern is using a Hash Table or Array to track moves per player, then validating wins efficiently without redundant scans. Clean interface design matters more than raw algorithm knowledge here.
Do I need to support variable board sizes?+
Depends on the interviewer. Read the problem statement carefully. Some codebases require you to generalize; others explicitly say 3x3. Asking clarifying questions upfront saves you a rewrite mid-interview. If it's not specified, assume 3x3 and mention that assumption.
How does this relate to Matrix and Array topics?+
You can represent the board as a 2D Array (Matrix) for simplicity, or use a Hash Table to store moves and avoid allocating a full grid. Array approach is more intuitive; Hash Table approach is cleaner for sparse or variable-size boards. Both are valid; trade off clarity for space efficiency.
What happens if someone makes an invalid move or plays out of turn?+
Handle it explicitly. Return false or throw an exception, not silently ignore it. Many candidates skip this detail. Interviewers notice. Show you're thinking about edge cases and robustness, not just the happy path.
Want the actual problem statement? View "Design Tic-Tac-Toe" on LeetCode →