学过的东西，
下次能自己讲清楚。
输入 $coach，从课程或你正在读的一章开始。教练安排今天的任务，依据实际回答追问、纠错，再接着上次练。
课程快照 2026-09-08.1。进入课程时检查公开版本；离线可继续用已有快照。部分 Cohort 作业待补充，各路线周次独立。
Cohort · verified Mock assignments
Only the first two Mock windows are verified. Mock week labels are independent of cohort calendar weeks. Coding weekly folder is unavailable; later assignments are not invented. No pairing or meeting details are included. Task themes were reviewed from the cohort schedule; the original private schedule, participant details and meeting access are not published.
coach，从 cohort 第 1 周开始，今天 30 分钟
Mock Week 1 · 3 tasks
- Technical disagreement BQ
Tell one concrete story, distinguish your own actions, and answer a skeptical follow-up.
- Subarray Sum Equals K Coding
Explain the approach, attempt independently, then handle a changed constraint.
- URL Shortener System Design
Explain the approach, attempt independently, then handle a changed constraint.
Mock Week 2 · 3 tasks
- Taking initiative BQ
Tell one concrete story, distinguish your own actions, and answer a skeptical follow-up.
- Permutation in String Coding
Explain the approach, attempt independently, then handle a changed constraint.
- News Feed System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 3 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 4 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 5 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 6 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 7 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 8 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 9 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 10 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 11 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
Week 12 · pending publication · 0 tasks
尚未取得正式作业。Coach 建议必须另行标注。
System Design · 9-week resource plan
Weekly focus summaries from the public plan. Task durations and acceptance targets are coach study slices, not official full-week workloads.
coach，从 system-design 第 1 周开始，今天 30 分钟
Week 1 · 1 tasks
- Requirements, capacity & URL Shortener System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 2 · 1 tasks
- News Feed: replication, indexes & caching System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 3 · 1 tasks
- Chat, notifications, rate limiting & geospatial System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 4 · 1 tasks
- Key-value store, file sync & consistency System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 5 · 1 tasks
- Transactions, orders & flash sale System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 6 · 1 tasks
- Streaming, aggregation & metrics System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 7 · 1 tasks
- Search, ranking & Top K System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 8 · 1 tasks
- Video/CDN; collaborative editor and scheduler mocks System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 9 · 1 tasks
- Integrate, mock and taper System Design
Explain the approach, attempt independently, then handle a changed constraint.
Coding · 6-week resource plan
Suggested sequencing from the public resource; not the inaccessible cohort weekly homework. Read the linked resource to choose a concrete problem.
coach，从 coding 第 1 周开始，今天 30 分钟
Week 1 · 1 tasks
- State maintenance & traversal foundations Coding
Explain the approach, attempt independently, then handle a changed constraint.
Week 2 · 1 tasks
- Continue state maintenance & traversal Coding
Explain the approach, attempt independently, then handle a changed constraint.
Week 3 · 1 tasks
- Ordering & binary search Coding
Explain the approach, attempt independently, then handle a changed constraint.
Week 4 · 1 tasks
- DP, object design & enumeration Coding
Explain the approach, attempt independently, then handle a changed constraint.
Week 5 · 1 tasks
- Review weak patterns Coding
Explain the approach, attempt independently, then handle a changed constraint.
Week 6 · 1 tasks
- Timed coding mocks Coding
Explain the approach, attempt independently, then handle a changed constraint.
Hello Interview · 12 周完整计划
保留原来的 Hello Interview 12 周公开计划：12 个周计划、84 个日计划。包含系统设计、算法及口述练习；原页面日期和时段是示例，按个人进度继续。这套公开日历与 Cohort、9 周计划及规范课程清单独立。
coach，从 legacy-system-design 第 1 周开始，今天 30 分钟
Week 1 · 7 tasks
- MON · 07.27 - Bitly：一次读到 High-Level Design System Design
Explain the approach, attempt independently, then handle a changed constraint.
- TUE · 07.28 - Bitly：把 Deep Dives 全部打穿 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- WED · 07.29 - Rate Limiter：一次读到 High-Level Design System Design
Explain the approach, attempt independently, then handle a changed constraint.
- THU · 07.30 - Rate Limiter：原子性、分片与故障策略 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- FRI · 07.31 - 横向串联：缓存、计数器与系统边界 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- SAT · 08.01 - 双项目 Mock：完整答题与压力追问 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- SUN · 08.02 - 验收、外部计划 Crosswalk 与 Week 2 预热 System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 2 · 7 tasks
- Week 2 Day 1 - Distributed Cache：先定义事实，再画读路径 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 2 - Distributed Cache：复制、分片、热点与故障 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 3 - Dropbox：把 blob path 与 metadata path 分开 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 4 - Dropbox：续传、提交、同步与冲突 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 5 - 横向迁移：读扩展、缓存与大对象的边界 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 6 - 完整 Mock：基础设施主线 + 应用压力轮 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 2 Day 7 - 证据验收、弱项修复与周级综合 System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 3 · 7 tasks
- 第 3 周 Day 1 - FB News Feed：先盲做需求/API/HLD，再读 live 目录 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 2 - FB News Feed：fan-out、celebrity skew、hot posts 与派生状态 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 3 - FB Live Comments：实时评论 HLD、SSE 与可恢复历史 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 4 - FB Live Comments：server coordination、mega streams、disconnect recovery System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 5 - Instagram：先盲做，再迁移 News Feed/Comments 的可复用与失效假设 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 6 - 双核心 Mock：News Feed 45 分钟 + Live Comments 45 分钟 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 3 周 Day 7 - Week 3 证据验收、弱项修复、停在 reviewer gate System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 4 · 7 tasks
- 第 4 周 Day 1 - WhatsApp：消息事实、connection ownership 与离线投递 HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 2 - WhatsApp：多设备、连接失败、Redis 丢投递、乱序与 last seen System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 3 - Google Docs：operation log、concurrent edits 与实时协同 HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 4 - Google Docs：WebSocket scale、storage compaction、load/update recovery System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 5 - Online Chess：先盲做，再迁移 messaging/collaboration 的可复用与失效假设 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 6 - 双核心独立 Mock：WhatsApp 45 分钟 + Google Docs 45 分钟 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 4 周 Day 7 - Week 4 证据验收、英语 recall、停在 reviewer gate System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 5 · 7 tasks
- 第 5 周 Day 1 - Ticketmaster HLD：seat、hold、order 与 payment 的权威边界 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 2 - Ticketmaster deep dives：reservation TTL、热门演出、搜索缓存与不超卖 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 3 - Online Auction：bid ledger、current highest bid 与强一致 HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 4 - Online Auction deep dives：ordering、durability、SSE 与 10M concurrent auctions System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 5 - Robinhood：ordered market updates、order gateway 与 financial retry failure System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 6 - Adaptive mock：Ticketmaster 45 分钟 + Auction/Robinhood pressure rounds System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 5 周 Day 7 - Week 5 synthesis：三域 winning transaction 与 duplicate/retry failure System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 6 · 7 tasks
- 第 6 周 Day 1 - Payment System：PaymentIntent、ledger truth 与 idempotent charge HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 2 - Payment System：immutable ledger、reconciliation、compensation 与 webhook safety System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 3 - Ad Click Aggregator：server-side redirect、event time 与 one-minute aggregate HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 4 - Ad Click Aggregator：at-least-once aggregation、late events、dedupe state 与 reconciliation System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 5 - Metrics Monitoring：series model、alert windows、cardinality 与 backpressure System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 6 - 三场 CORE mock：Payment、Ad Click、Metrics 各 45 分钟 + 两个 deep dives System Design
Explain the approach, attempt independently, then handle a changed constraint.
- 第 6 周 Day 7 - Week 6 synthesis：修复最弱回答，收敛 source/link/artifact/visual gate System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 7 · 7 tasks
- Week 7 Day 1 - YouTube CORE: upload, publication state, and streaming HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 2 - YouTube CORE: resumable upload, failed upload, transcode orchestration, CDN invalidation System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 3 - YouTube Top K FULL: all-time and tumbling-window HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 4 - YouTube Top K FULL: stream aggregation, late events, approximate/exact materialized views System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 5 - Strava TRANSFER: blind activity ingestion, offline replay, stale derived views System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 6 - Adaptive mock: YouTube CORE plus Top K pressure round System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 7 Day 7 - Week 7 synthesis: replay, derived views, idempotency, operations gate System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 8 · 7 tasks
- Week 8 Day 1 · Web Crawler CORE HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 2 · Web Crawler CORE Deep Dives System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 3 · Job Scheduler CORE HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 4 · Job Scheduler CORE Deep Dives System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 5 · Price Tracking Service TRANSFER System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 6 · Two 45-minute Adaptive Mocks System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 8 Day 7 · Repair, Synthesis, Scorecard System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 9 · 7 tasks
- Day 1 - FB Post Search FULL: attempt, requirements and HLD System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 2 - FB Post Search FULL: deep dives, writes and privacy freshness System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 3 - News Aggregator TRANSFER: blind attempt and HLD delta System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 4 - News Aggregator TRANSFER: pagination, low latency and freshness System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 5 - Yelp TRANSFER: blind attempt and geo candidate retrieval System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 6 - Yelp TRANSFER: reviews, abuse, geo pagination and mock System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Day 7 - Week 9 repair, synthesis and READY_FOR_REVIEW System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 10 · 7 tasks
- Week 10 Day 1 - Uber HLD: fare, ride request, location update, candidate match System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 2 - Uber deep dives: geo index, freshness, driver reservation, durable dispatch System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 3 - Tinder full: profile preferences, geo feed, swipe, mutual match System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 4 - Tinder deep dives: atomic mutual match, feed generation, stale cache, Bloom filter System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 5 - Local Delivery full: availability, nearby DCs, inventory reservation System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 6 - Adaptive mock: Uber 45m plus Tinder and Local Delivery pressure rounds System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 10 Day 7 - Synthesis and repair: stale facts, reservations, races, observability System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 11 · 7 tasks
- Week 11 Day 1 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 2 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 3 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 4 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 5 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 6 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 11 Day 7 System Design
Explain the approach, attempt independently, then handle a changed constraint.
Week 12 · 7 tasks
- Week 12 Day 1 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 2 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 3 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 4 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 5 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 6 System Design
Explain the approach, attempt independently, then handle a changed constraint.
- Week 12 Day 7 System Design
Explain the approach, attempt independently, then handle a changed constraint.