Citadel Coding Interview Questions
25 Citadel 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 Citadel interviewer values, and a FAQ section.
Showing 2 problems of 25
- #146mediumvery frequently asked
146. LRU Cache
LRU Cache is directly relevant to Citadel's systems work: caching market data, reference data (security master), and computed risk metrics all require eviction policies. Citadel interviewers use this to verify you can compose a hash map and doubly-linked list into O(1) get and put — and that you understand why each structure is necessary.
- #295mediumvery frequently asked
295. Find Median from Data Stream
Computing a running median over a live data stream is a real operational metric at Citadel — median latency of order acknowledgements, median fill rate over a rolling window, median bid-ask spread. The two-heap technique is the standard interview answer, but Citadel pushes hard on the rebalancing logic and on what happens at O(log n) vs O(n).