5-day plan

The prep doc's ten-day plan, compressed to five and pointed at the content built here. Each link opens a verified lab, problem, design topic, or speaking prompt.

1. Day 1Warm up + the canonical screens
   • ·Java one-file warmup (enum, Map/Set, main() tests) — 30 min, no AI
   • →KeyValueStore with TTL (logical time) — the canonical Opendoor screen
   • →LRU / TTL cache
   • →Say it out loud: status codes 404 / 409 / 400
2. Day 2State machines (the Opendoor core)
   • →Offer / Transaction FSM — flagship: status = business event, 409, audit
   • →Ops Task Board state machine (claim / start / complete)
   • →Say it out loud: the transition endpoint (the crux)
   • →Say it out loud: design the offer API
3. Day 3Concurrency + idempotency (money correctness)
   • →Idempotency store — a retried charge must not double-apply
   • →Row-level lock — duplicate ID generator (your SK AX bullet)
   • →Optimistic lock — version conflict on concurrent edits
   • →Distributed lock — no double cross-server execution (ShedLock)
   • →Transaction event processor — dedup eventId + out-of-order
4. Day 4Data jobs + system design
   • →Inventory ↔ financial reconciler (your staging-table bullet)
   • →Pricing rule engine (base + renovation + risk + market, breakdown)
   • →System design: Ops Task Board + Home Transaction Workflow
   • →Say it out loud: staging table + batch worker
5. Day 5Mocks + communication polish
   • →AI-enabled coding mock — catch the fallible pair's bugs (needs API key)
   • →System design full mock: Pricing, Reconciliation, Real-time
   • →Record the résumé deep-dives out loud (distributed-lock, LLM pipeline, PK-payload)
   • →Home search insurance problem