Roblox Software Engineer Onsite Coding Questions

See here for the previous interview: https://www.1point3acres.com/bbs/thread-1146238-1-1.html This round consisted of one coding question and one Subject Design question. The coding question was about

Given a user's name and a domain, generate a normalized email address. The user's name may include spaces and other symbols which need to be handled. For example, if the user's name is 'John Doe' and

LeetCode #723: Candy Crush. Difficulty: Medium. Topics: Array, Two Pointers, Matrix, Simulation. Asked at Roblox in the last 6 months.

LeetCode #1434: Number of Ways to Wear Different Hats to Each Other. Difficulty: Hard. Topics: Array, Dynamic Programming, Bit Manipulation, Bitmask. Asked at Roblox in the last 6 months.

LeetCode #359: Logger Rate Limiter. Difficulty: Easy. Topics: Hash Table, Design, Data Stream. Asked at Roblox in the last 6 months.

LeetCode #210: Course Schedule II. Difficulty: Medium. Topics: Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort. Asked at Roblox in the last 6 months.

LeetCode #642: Design Search Autocomplete System. Difficulty: Hard. Topics: String, Depth-First Search, Design, Trie, Sorting, Heap (Priority Queue), Data Stream. Asked at Roblox in the last 6 months.

LeetCode #68: Text Justification. Difficulty: Hard. Topics: Array, String, Simulation. Asked at Roblox in the last 6 months.

LeetCode #2817: Minimum Absolute Difference Between Elements With Constraint. Difficulty: Medium. Topics: Array, Binary Search, Ordered Set. Asked at Roblox in the last 6 months.

LeetCode #48: Rotate Image. Difficulty: Medium. Topics: Array, Math, Matrix. Asked at Roblox in the last 6 months.

LeetCode #362: Design Hit Counter. Difficulty: Medium. Topics: Array, Binary Search, Design, Queue, Data Stream. Asked at Roblox in the last 6 months.

LeetCode #2672: Number of Adjacent Elements With the Same Color. Difficulty: Medium. Topics: Array. Asked at Roblox in the last 6 months.

LeetCode #1: Two Sum. Difficulty: Easy. Topics: Array, Hash Table. Asked at Roblox in the last 6 months.

LeetCode #933: Number of Recent Calls. Difficulty: Easy. Topics: Design, Queue, Data Stream. Asked at Roblox in the last 6 months.

## Problem Segment a string or array into valid parts satisfying given rules, likely a DP word break-style problem. ## Tags dynamic_programming, strings, arrays

## Problem You have a `user_logs` table with millions of rows. Implement pagination using keyset (cursor) pagination, which is more efficient than OFFSET for large datasets. **Schema:** ```sql CREATE TABLE user_logs ( log_id BIGINT PRIMARY KEY AUTO_INCREMENT, user_id BIGINT NOT NULL, action VARCHAR(64), logged_at TIMESTAMP NOT NULL, INDEX idx_user_logged (user_id, logged_at DESC, log_id DESC) ); ``` **API:** `GET /users/:id/logs?cursor=<token>&limit=20` Write the SQL for the first page and subsequent pages. ```sql -- First page SELECT * FROM user_logs WHERE user_id = ? ORDER BY logged_at DESC, log_id DESC LIMIT 20; -- Next page (cursor encodes last_logged_at and last_log_id) SELECT * FROM user_logs WHERE user_id = ? AND (logged_at, log_id) < (?, ?) ORDER BY logged_at DESC, log_id DESC LIMIT 20; ``` ## Follow-ups 1. Why is `(logged_at, log_id) < (?, ?)` correct even when two logs share the same timestamp? 2. Compare OFFSET vs. keyset pagination for the 10,000th page of results. 3. How would you encode the cursor as an opaque token to hide implementation details from clients? 4. What index does MySQL use for the keyset query, and how would you verify it with EXPLAIN?

## Problem: Build an Image Feed (Infinite Scroll + Offline Support + Testing) You are given an API to fetch a paginated list of images. Implement a frontend **Image Feed** page/component with the fol

Building on Part 1, each request now contains multiple fields (e.g., `userId`, `deviceId`, `endpoint`). You need to rate limit each field separately, with multiple dimensions enforced simultaneously.

Implement a rate limiter that decides whether each incoming request should be allowed at a given timestamp. Design an interface/class that supports request admission: - Each request contains a key `

## Problem: Implement a Rate Limiter (with follow-up) Design and implement a **Rate Limiter** that controls the rate at which requests are allowed. ### Core requirement Given a rule: within any con