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Hectal

Phase 15 · Interview Mastery

The two templates

You never improvise an interview again. Run these in order, out loud, on every prompt — whatever the system. Print them, tape them to a wall, and practice until they run in your sleep.

HLD — 13 steps

  1. 01Requirements — Functional + non-functional, written down. Ask the 8 questions from Phase 0.
  2. 02Scale estimation — QPS, peak, storage, bandwidth, memory — order-of-magnitude math.
  3. 03APIs — Verbs, paths, request/response shapes, status codes.
  4. 04Data model — Core tables + access patterns + consistency budget per path.
  5. 05High-level architecture — Clients, LB, services, data stores, queues, caches, CDN.
  6. 06Core request flow — One write path + one read path traced through the boxes.
  7. 07Bottlenecks — Name the top two constraints with numbers (write hot spot, DB, bandwidth).
  8. 08Scaling solution — Reads → cache/replicas/CDN; writes → partition/queue; measure each.
  9. 09Failure handling — Node death, dependency timeout, queue overflow, region failure.
  10. 10Consistency — Per-path: strong vs eventual; read-your-writes; outbox/saga where needed.
  11. 11Security — Auth flow, mTLS, PII/tenancy, rate limits.
  12. 12Monitoring — Golden signals + trace/log correlation.
  13. 13Trade-offs — Top 3 decisions and the explicit cost of each — what you'd reconsider.
Full lesson with runnable script →

LLD — 13 parts

  1. 01Requirements — Written, with edge cases — the requirement-analysis drill.
  2. 02Actors — Who uses it: attendant, driver, admin, system.
  3. 03Use cases — The 4–6 core flows, one line each.
  4. 04Entities — Nouns with identity + state; underline them from the prompt.
  5. 05Responsibilities — Which class owns which behavior — the most important LLD skill.
  6. 06Relationships — 1:1, 1:N, N:N, composition vs aggregation vs association.
  7. 07Interfaces — The seams where extensions plug in.
  8. 08SOLID — The violations your design explicitly avoids.
  9. 09Design patterns — Pick for a concrete problem — strategy, state, factory, observer.
  10. 10Extensibility — What changes when a new variation arrives — walk the files.
  11. 11Concurrency — Shared-state audit + the atomic operation choice.
  12. 12Code — Production-quality Java, not a script.
  13. 13Test cases — Unit tests for the invariants + edge cases.
Full lesson with runnable script →

How to actually use these

The templates are a timing discipline: HLD in ~30 minutes (numbers by minute 5), LLD in ~25. Run each on a timer with the syllabus closed. When you can deliver both from memory on an unfamiliar system, you are done — that is the syllabus's completion checklist, verbatim.

Practice with real drillsFollow the first 10 sessions