Microsoft

"You are implementing a lock-free Single-Producer Multi-Consumer (SPMC) ring buffer for high-frequency market data": The interviewer asked me how to eliminate CPU lock contention and avoid false sharing across cores; I walked through an implementation using atomic compare-and-swap (CAS) sequences with memory-order release/acquire fences, explicit 64-byte cache line padding between head and tail pointers, and sequence-stamped counters to circumvent the ABA problem. "An autonomous drone with noisy LiDAR and accelerometer telemetry must localize itself while mapping an unfamiliar subterranean tunnel": I was asked to formulate a real-time state estimator that prevents drift when landmark readings drop out; I modeled it as a Pose-Graph SLAM problem, employing an Extended Kalman Filter (EKF) for local odometry fusion and sparse bundle adjustment via the Levenberg-Marquardt optimizer to detect loop closures and correct accumulated drift. "Design an approximate nearest-neighbor vector search engine to serve semantic embeddings with sub-10ms p99 latency across billions of vectors": The interviewer challenged me on why exact brute-force Euclidean distance fails at scale; I broke down the construction of a Hierarchical Navigable Small World (HNSW) graph, detailing how multi-layer probabilistic skip-lists guide greedy beam searches through dense vector clusters alongside product quantization (PQ) for in-memory compression.