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.
Showing 16 problems of 25
- #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 → - #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 → - #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 → - #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 → - #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 → - #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 → - #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 → - #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 →
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