Redis Coding Interview Questions
25 Redis coding interview problems with full optimal solutions — 8 easy, 12 medium, 5 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Redis interviewer values, and a FAQ section.
Showing 12 problems of 25
- #9mediumfoundational
9. LRU Cache
Design a fixed-capacity Least-Recently-Used cache with O(1) get/put; this is the most asked Redis interview question because it mirrors maxmemory-policy allkeys-lru.
- #10mediumfoundational
10. Number of Islands
Count connected '1' regions in a 2D grid; Redis uses it to verify clean BFS/DFS hygiene before discussing cluster-partition reconnection.
- #11mediumfoundational
11. Kth Largest Element in an Array
Find the kth largest value; Redis interviewers use it to probe heap intuition that mirrors how ZSETs maintain top-K rankings.
- #12mediumfoundational
12. Top K Frequent Elements
Return the k most frequent integers; Redis uses it to probe bucket-sort and heap thinking, the same patterns powering Redis Streams XAUTOCLAIM and ZSET top-K queries.
- #13mediumfoundational
13. Design Twitter
Implement a simplified Twitter with postTweet, getNewsFeed, follow, unfollow; Redis loves it because the optimal solution is the Redis fan-out-on-read pattern.
- #14mediumfoundational
14. Insert Delete GetRandom O(1)
Design a set supporting insert, remove and getRandom all in O(1); Redis loves it because SRANDMEMBER and dict-table sampling use the same trick.
- #16mediumfoundational
16. Task Scheduler
Compute the minimum CPU cycles to execute tasks with a cool-down constraint; Redis uses it to probe scheduling logic that mirrors expiration sampling in cron.c.
- #17mediumfoundational
17. Snapshot Array
Implement an array with O(1) set/snap and O(log) snapshot reads; Redis uses it because the data structure mirrors how RDB snapshots cooperate with copy-on-write forks.
- #18mediumfoundational
18. Design Underground System
Track passenger check-in/check-out and compute average travel times; Redis uses it to test hash and counter aggregation patterns close to Streams + HINCRBYFLOAT.
- #19mediumfoundational
19. Time Based Key-Value Store
Implement a KV store that returns the most recent value with timestamp <= query; Redis loves it because it mirrors ZADD + ZREVRANGEBYSCORE patterns for time-series.
- #20mediumfoundational
20. Subarray Sum Equals K
Count the number of contiguous subarrays that sum to k; Redis uses it to test prefix-sum + hashmap intuition, the same trick that powers GETSET cumulative counters.
- #21mediumfoundational
21. Word Break
Decide whether a string can be segmented into space-separated dictionary words; Redis uses it as a DP/memoization probe that overlaps with how the engine matches CONFIG GET glob patterns.