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 2026-09-13.1 随安装包提供。未配置公共端点时，刷新保持离线。
系统设计，从需求一步步推导到深挖
Functional Requirements → Non-functional Requirements → Core Entities → Data Flow → API / System Interface → High Level Design → Deep Dives
陪读先讲当前环节再检查理解；练习先自己作答；Mock 由你主导、结束后复盘；复测回到已记录的薄弱环节。保存当前阶段和下一步，下次接着学。
参考 Hello Interview Delivery Framework。原文先 API、后可选 Data Flow；这里默认先梳理数据流，再定义 API。陪读指定文章时跟随原文顺序。
$coach 陪我学 News Feed，从 Functional Requirements 开始
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. 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.