Roblox Interview Questions — Page 3

Roblox·Software Engineer·Technical Phone Screen

Apr 2026

Roblox software engineer interview with a scheduling/subset selection problem. Pretty algorithmic, nothing too wild, but the constraints tripped me up at first.

Given a list of events in input order, select a subset where no two chosen events are adjacent (indices at least 2 apart). You may also have a minimum count requirement. Return whether a valid selection exists, and if so, provide one valid schedule.

“Took me a minute to realize the greedy approach was fine here.”

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Roblox·Software Engineer·Technical Phone Screen

Apr 2026

Roblox software engineer interview with a data structures / systems angle. The core problem was about finding the most frequent path in a stream of API call logs, and it escalated pretty quickly into streaming and approximation territory.

Given a list of API call traces where each trace is a sequence of endpoints, write a function that returns the most frequently occurring path.
How would you extend the solution to return the top-K most frequent paths instead of just the single most frequent one?
If the input is a continuous stream and you can't hold all traces in memory, how would you approximate the top-K frequent paths?

“The base problem is just a frequency count with a hash map, nothing crazy.”

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Roblox·Data Scientist·Technical Phone Screen

Apr 2026

A Roblox data science interview that was essentially one massive observational study design question. No A/B test allowed, no easy out, just a full end-to-end causal inference problem about local creators. Dense and exhausting.

You can't run an A/B test. Define 'local creators' as creators whose games match a player's native language. Design a full observational study to estimate whether players prefer local creators, covering metric choice, unit of analysis, sessionization, causal identification strategy, covariate matching, instrument selection, robustness checks, and the SQL schema you'd need.

“This was basically seven questions stapled together and handed to me as one.”

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Roblox·Software Engineer·Technical Phone Screen

Apr 2026

Roblox software engineer interview with a randomized partitioning problem that sounds deceptively simple but has a few layers to it once you get into the complexity and testing discussion.

Given a list of integers and an integer k, write a function that randomly partitions the list into k non-empty segments and returns a list of lists. Walk through your approach, analyze the time and space complexity, and explain how you'd verify that the result is actually random.

“The coding part wasn't too bad.”

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Roblox·Data Scientist·Technical Phone Screen

Apr 2026

Roblox data scientist interview that went deep into scheduling theory, which I was not expecting at all. The problem felt more like an operations research PhD qualifying exam than anything I'd call a typical DS interview.

You have two parallel assembly stations with sequence-dependent setup times, a precedence constraint between two jobs, and a planned downtime window on one station. How would you argue that this scheduling problem is NP-hard?
Given the specific instance with three jobs, two stations, known processing and setup times, a precedence constraint that J2 cannot start before J1 finishes, and a maintenance window on S1 from t=60 to t=70, compute the optimal schedule with explicit start and finish times per station and the final makespan.
For the general version of this problem with n jobs and m stations, propose a practical solver. You can use an integer program, a metaheuristic, or both. Discuss complexity, any pruning strategies, and what approximation guarantees or bounds you can claim.

“I knew the general argument, something about reducing from 3-partition or relating it to flow-shop with SDST, but I fumbled trying to be precise about which known hard variant this maps to.”

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Roblox·Frontend Engineer·Onsite - System Design / Architecture

Apr 2026

System design round at Roblox for a frontend engineer role, focused entirely on designing a reusable dropdown/select component for a component library. Pretty deep dive, they pushed hard on accessibility and positioning edge cases.

Design a reusable dropdown menu component for a shared UI library. Walk through the public API, accessibility model, and how the floating list is rendered and positioned.
Is this component a menu (list of actions) or a select/listbox (value selection)? How does that distinction affect your design?
How would you handle the accessibility and keyboard interaction model? Specifically, does DOM focus move into the list or stay on the trigger?
How would you render and position the popup so it doesn't get clipped inside a scrollable modal or an overflow:hidden container?
The option list could have thousands of items or be loaded asynchronously. How do you keep the component performant?
How would you extend this to support multi-select with checkboxes and a summarized trigger label?
How would you make the option list searchable with server-side filtering, and what would you debounce or cache?

“This was the main question and it sprawled across like three sub-topics.”

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Roblox·Software Engineer·Technical Phone Screen

May 2026

Roblox software engineer round, one coding question the whole time. The problem looked like a frequency counter at first glance but the tie-breaking rules added enough wrinkles to slow me down.

You're given a list of call stack snapshots from a sampling profiler, where each snapshot is an ordered list of function names from outermost to innermost caller. Find the call stack that appears most frequently. If there's a tie, prefer the deeper stack, and if still tied, prefer the lexicographically smaller one. Then extend your solution to handle multiple threads, returning the most frequent stack per thread.

“The base case came together fast, just convert each stack to a tuple, count with a dict, then sort or reduce with the tie-break logic.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Roblox for a software engineer role. The core problem was designing the backend for that little social proof line you see on a game page, something like 'Alice, Bob, and 12,345 people have played this.' Deceptively simple on the surface but it pulls in a lot of moving parts once you start thinking about scale.

Design the backend system that powers a personalized social proof line on a game's detail page, showing the viewer's friends who played and a total unique player count.
How do you deduplicate play events so that a single user's multiple sessions only count as one unique player, especially given at-least-once event delivery?
How do you handle write pressure on a single game's player count when that game goes viral and thousands of events per second converge on the same counter?
If a user has millions of friends (think a celebrity account), how do you keep the friends-who-played intersection fast without scanning the entire friend list?
How would your design change if the product requirement shifted from 'total players ever' to 'players who played this week' using a sliding time window?
A bug caused an hour of play events to be double-published. Walk through whether your design absorbs this or how you'd repair the count.
What clarifying questions would you ask before designing this system, and what assumptions are you making about the definition of 'played' and the privacy rules around showing friend names?

“This one looked like a display problem until I actually started drawing it out.”

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Roblox·Machine Learning Engineer·Technical Phone Screen

May 2026

Roblox ML engineer interview had me extending a classic leetcode problem into something with real system design teeth. The follow-up questions about concurrency and memory cleanup were where it got interesting.

Extend a basic hit counter to support per-user rate limiting: implement hit(userId, timestamp) and getHits(userId, timestamp) where getHits returns the count of hits in the last 5 minutes for that user.
How would you handle memory cleanup for users who haven't had any activity in a long time?
How would you make this hit counter thread-safe under concurrent calls?
How would you extend this design to support a configurable time window instead of a hardcoded 5-minute limit?

“I went straight to a dictionary of deques, which was the right call, but I fumbled a bit explaining the sliding window cleanup inside getHits.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Roblox for a software engineer role. The question was all about scheduled payments, which sounds straightforward until you actually have to think through the full reliability story.

Design a payment system that supports scheduled (delayed) payments, where users can set a payment to execute at a future time. Address persistent storage, reliable triggering, idempotency, retry behavior on transient failures, exactly-once execution guarantees, and consistency vs latency trade-offs at scale.

“This one had a lot of surface area and I think I spread myself too thin early on.”

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