Robinhood Coding Interview Questions
25 Robinhood coding interview problems with full optimal solutions — 5 easy, 16 medium, 4 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Robinhood interviewer values, and a FAQ section.
- #1easyfoundational
1. Two Sum
Two Sum is Robinhood's most reliable phone-screen warm-up: given an integer array and a target, return the indices of the two numbers that sum to the target. The interviewer is watching whether you narrate the brute-force-to-hash-map tradeoff before coding the optimal.
3 free resourcesSolve → - #3mediumfrequently asked
3. Longest Substring Without Repeating Characters
Given a string, find the length of the longest substring without repeating characters. Robinhood asks this to test the sliding-window-with-hash-map pattern — the same shape they use in production for de-duped event streams.
3 free resourcesSolve → - #15mediumfrequently asked
15. Three Sum
Given an array of integers, find all unique triplets that sum to zero. Robinhood asks this as the universal follow-up to Two Sum — they want to see the sort + fix-one + two-pointer pattern executed cleanly with duplicate handling.
3 free resourcesSolve → - #20easyfoundational
20. Valid Parentheses
Given a string of brackets, determine whether the string is valid. At Robinhood this is a classic 15-minute warm-up that tests whether you reach for a stack instantly and handle empty-stack edge cases without prompting.
3 free resourcesSolve → - #23hardfrequently asked
23. Merge k Sorted Lists
Given an array of k sorted linked lists, merge them into one sorted list. Robinhood asks this as the canonical heap-of-streams problem — it maps directly to merging k sorted streams of trades or price-feed events.
4 free resourcesSolve → - #33mediumfrequently asked
33. Search in Rotated Sorted Array
Given a rotated sorted array, find a target value in O(log n). Robinhood asks this as the natural follow-up to binary search — they want to see the modified binary-search that identifies the sorted half first.
3 free resourcesSolve → - #42hardfrequently asked
42. Trapping Rain Water
Given heights representing an elevation map, compute how much water it can trap after raining. Robinhood asks this as a hard-tier classical problem to see whether you reach for two-pointer over DP-of-max-arrays, and whether you can articulate the invariant cleanly.
3 free resourcesSolve → - #49mediumfrequently asked
49. Group Anagrams
Given an array of strings, group the anagrams together. Robinhood asks this to test hash-key design: the right answer is to pick a canonical form (sorted chars or char-count signature) and bucket by it.
3 free resourcesSolve → - #53mediumfoundational
53. Maximum Subarray
Given an integer array, find the contiguous subarray with the largest sum. Robinhood asks this for two reasons: Kadane's algorithm is interview-classic and the daily-delta variant maps directly to best-trade-window questions on the trading side.
3 free resourcesSolve → - #56mediumfrequently asked
56. Merge Intervals
Given a list of intervals, merge overlapping ones. Robinhood asks this to test interval reasoning that maps directly to consolidating trade windows, market-data ticks, and scheduling jobs across overlapping price-feed batches.
3 free resourcesSolve → - #121easycompany favorite
121. Best Time to Buy and Sell Stock
Given an array of daily stock prices, return the maximum profit from a single buy and sell. This is the most thematically on-brand question Robinhood asks — and they ask it specifically to test whether you reach for the one-pass min-tracking trick versus a brute-force pair search.
3 free resourcesSolve → - #122mediumfrequently asked
122. Best Time to Buy and Sell Stock II
Same setup as Best Time I but with unlimited transactions. Robinhood asks this as the natural follow-up — the optimal collapses to a one-line sum that surprises candidates who reach for DP first.
3 free resourcesSolve → - #128mediumfrequently asked
128. Longest Consecutive Sequence
Given an unsorted array of integers, return the length of the longest consecutive elements sequence. Robinhood asks this for the surprise O(n) insight — sort feels right but the hash-set trick beats it cleanly.
3 free resourcesSolve → - #146mediumcompany favorite
146. LRU Cache
Design an LRU cache that supports get and put in O(1). Robinhood asks this because hot-path market-data services rely on bounded eviction caches — the right answer is a doubly-linked list plus a hash map, not just one of the two.
4 free resourcesSolve → - #200mediumfrequently asked
200. Number of Islands
Given a 2D grid of '1's (land) and '0's (water), count the number of islands. Robinhood asks this as the canonical graph-traversal problem; the right answer is BFS/DFS over a 4-connected grid with a clean visited-marking strategy.
4 free resourcesSolve → - #206easyfoundational
206. Reverse Linked List
Given the head of a singly linked list, reverse the list and return the new head. Robinhood asks this as a 10-minute warm-up on phone screens — they're checking pointer fluency and whether you can do it iteratively without leaking nodes.
3 free resourcesSolve → - #207mediumfrequently asked
207. Course Schedule
Given a graph of course prerequisites, determine if it's possible to finish all courses. Robinhood asks this for cycle-detection on a directed graph — the same shape that pops up in dependency resolution for service deploys and ETL DAGs.
4 free resourcesSolve → - #239hardfrequently asked
239. Sliding Window Maximum
Given an array and a window size k, return an array of the maximum in each sliding window of size k. Robinhood asks this because rolling-max patterns power high-watermark queries in market-data analytics and order-book monitoring.
3 free resourcesSolve → - #253mediumfrequently asked
253. Meeting Rooms II
Given an array of meeting time intervals, return the minimum number of conference rooms required. Robinhood asks this because the same shape — concurrent-task counting — powers capacity planning for trading workers and order-execution pools.
3 free resourcesSolve → - #295hardfrequently asked
295. Find Median from Data Stream
Design a streaming structure that supports addNum and findMedian. Robinhood asks this because the two-heap pattern maps directly to real-time price-feed statistics and rolling-window analytics on trade data.
3 free resourcesSolve → - #347mediumfrequently asked
347. Top K Frequent Elements
Given an integer array and integer k, return the k most frequent elements. Robinhood likes this for top-K pattern practice and as a natural lead-in to a discussion about how you'd track top-K ticker symbols by trade volume in real time.
3 free resourcesSolve → - #359easyfrequently asked
359. Logger Rate Limiter
Design a logger system that returns whether a unique message should be printed in a given timestamp; the same message cannot reprint within 10 seconds. Robinhood asks rate-limit design because production trading services need request throttles that can't break under load.
3 free resourcesSolve → - #362mediumfrequently asked
362. Design Hit Counter
Design a hit counter that counts the number of hits received in the past 5 minutes. Robinhood asks this because rolling-window counters are a daily-bread primitive for trading-system telemetry and abuse detection on order-placement APIs.
3 free resourcesSolve → - #380mediumfrequently asked
380. Insert Delete GetRandom O(1)
Design a data structure that supports insert, delete, and getRandom — all in average O(1). Robinhood likes this design problem because it forces you to combine an array (random access) with a hash map (membership / index lookup) cleanly.
3 free resourcesSolve → - #973mediumfrequently asked
973. K Closest Points to Origin
Given an array of points and integer k, return the k closest points to the origin. Robinhood asks the top-K family to test whether you reach for a max-heap of size k versus sort, and whether you cite the squared-distance optimization unprompted.
4 free resourcesSolve →
Related interview-prep guides
CodeSignal GCA for Tech Interviews in 2026: The Complete Guide
The CodeSignal General Coding Assessment is a 70-minute, four-task timed test scored on a 600 to 850 scale, used as a filter by Goldman Sachs, Capital One, Robinhood, Brex, and a growing list of tech and finance employers. This guide breaks down what it tests, how it scores, what it records during your session, and how to practice for it.
Karat Technical Interview Guide 2026: How the Third-Party Loop Actually Works
Karat is technical-interview-as-a-service. Karat-employed engineers run the technical loop for the hiring company in Karat's own recorded video and coding environment. The dynamic is different from an in-house interview: the interviewer is a contractor, not a future teammate, the rubric is fixed, the session is recorded for asynchronous review, and the hiring team's engineers watch the playback a day later. This guide is the practical map of how that loop works in 2026 and how to prepare for it.
CodeInterview.io Live Coding Interview Guide (2026): What the Platform Tracks and How to Walk Through It Cleanly
CodeInterview.io is a browser-based collaborative live-coding platform. Think of it as a lighter-footprint alternative to CoderPad with an integrated video call, per-keystroke replay, and a drawing whiteboard. Smaller market share than CoderPad but shows up at a meaningful slice of YC startups and mid-market tech teams in 2026. This is what CodeInterview.io tracks, how its all-in-one workflow compares to CoderPad, and how to walk through a live round cleanly.