The hardest interview problems that combine multiple domains and require expert-level architectural thinking
Design the complete ride-sharing backend: real-time GPS tracking (750K updates/sec), driver matching algorithms, surge pricing, payment processing, and multi-region operations for 50M trips/day.
Design ticket booking handling 10M concurrent users during on-sales, virtual queues, optimistic locking for inventory, bot detection, and 100x traffic spikes.
Design a search engine: distributed crawling (40K pages/sec), 100PB inverted index, PageRank computation, multi-stage ranking (BM25 + ML), serving 8B queries/day.
Design a trading platform with lock-free matching engine (<1ms latency), kernel bypass networking (DPDK), co-location, and SEC/FINRA regulatory compliance.
Design Kubernetes: control plane (API server, etcd, scheduler), pod scheduling across 5K nodes, service discovery, CNI networking, and RBAC security.