Riot Games Coding Interview Questions
25 Riot Games coding interview problems with full optimal solutions — 13 easy, 9 medium, 3 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Riot Games interviewer values, and a FAQ section.
- #1easyfoundational
1. Two Sum
Find two indices in an array whose values sum to a target — a hash-map warm-up at Riot before pivoting to matchmaking systems.
- #2easyfoundational
2. Valid Parentheses
Validate balanced brackets with a stack — Riot uses this to gauge stack fluency before chat-protocol parsing questions.
- #3easyfoundational
3. Merge Two Sorted Lists
Merge two sorted linked lists into one — Riot uses this to test pointer hygiene before queue-merge matchmaking questions.
- #4easyfoundational
4. Remove Duplicates from Sorted Array
Compact a sorted array in place — Riot uses this for two-pointer fluency before state-replication delta questions.
- #5easyfoundational
5. Remove Element
Filter an array in place by value — Riot uses this to test write-pointer mechanics before anti-cheat blacklist filtering questions.
- #6easyfoundational
6. Search Insert Position
Find where to insert a value in a sorted array — Riot uses this for binary-search fluency before MMR bucket lookup questions.
- #7easyfoundational
7. Maximum Subarray
Find the contiguous subarray with the largest sum — Riot uses Kadane to probe DP intuition before damage-window analytics questions.
- #8easyfoundational
8. Plus One
Increment a big-integer represented as a digit array — Riot uses this for carry-handling fluency before frame-counter arithmetic questions.
- #9easyfoundational
9. Same Tree
Compare two binary trees node-by-node — a recursion warm-up before Riot dives into client/server state-replication problems.
- #10easyfoundational
10. Single Number
Find the only element that appears once in an array where every other element appears twice — a bitwise trick Riot favors for low-overhead anti-cheat heuristics.
- #11easyfoundational
11. Linked List Cycle
Detect whether a singly linked list contains a cycle — Floyd's tortoise-and-hare is the canonical low-memory check Riot uses for replication-graph loops.
- #12easyfoundational
12. Majority Element
Find the element that appears more than n/2 times — Boyer-Moore voting is a Riot favorite because it surfaces dominant patterns in chat-spam and anti-cheat telemetry.
- #13easyfoundational
13. Reverse Linked List
Reverse a singly linked list in place — a pointer-manipulation warm-up Riot uses before scaling up to replay-buffer reversal questions.
- #14mediumfoundational
14. LRU Cache
Design a cache that evicts the least-recently-used key when capacity is hit — Riot's matchmaking and asset-streaming systems both lean on LRU eviction.
- #15mediumfoundational
15. Number of Islands
Count connected components of land on a 2D grid — Riot uses the same flood-fill structure for map-region partitioning and minimap pathfinding.
- #16mediumfoundational
16. Course Schedule
Detect whether a set of prerequisite pairs forms a valid DAG — Riot evaluates topological reasoning to model champion-ability dependency graphs and rune unlocks.
- #17mediumfoundational
17. Kth Largest Element in an Array
Return the kth largest element in an unsorted array — Riot tests this pattern when reasoning about leaderboard top-k queries and Elo bucket cutoffs.
- #18mediumfoundational
18. Coin Change
Find the fewest coins that sum to a target amount — Riot uses this DP pattern for RP-shop bundling and rune-page cost optimization.
- #19mediumfoundational
19. Top K Frequent Elements
Return the k most frequent elements in an array — a Riot favorite for telemetry-rollup and anti-cheat anomaly detection pipelines.
- #20mediumfoundational
20. Subarray Sum Equals K
Count contiguous subarrays whose sum equals k — Riot reaches for prefix-sum tricks when scanning telemetry streams for suspicious damage-windows.
- #21mediumfoundational
21. Daily Temperatures
For each day, find how many days until a warmer temperature — Riot uses the monotonic stack pattern when reasoning about next-event-time queries on server tick logs.
- #22mediumfoundational
22. Rotting Oranges
Compute the minutes until every fresh orange rots given multi-source spread — Riot tests multi-source BFS to reason about ability radii expanding over server ticks.
- #23hardfoundational
23. Find Median from Data Stream
Design a structure that returns the median of a streaming sequence — Riot uses two-heap streaming medians to track rolling Elo/Glicko percentile windows.
- #24hardfoundational
24. LFU Cache
Design an O(1) least-frequently-used cache — Riot favors LFU over LRU when caching match-history queries that exhibit heavy-tail access patterns.
- #25hardfoundational
25. Sliding Window Maximum
Return the maximum of every sliding window of size k — Riot uses monotonic deques to track peak damage or ping spikes within rolling server-tick windows.