WEEK 09 · 2026.09.21-09.27 · WRITER GATE
Day 4 - News Aggregator TRANSFER: pagination, low latency and freshness
2026-09-24 · THU · 补齐 News deep dives：stable cursor、<200ms feed、30min freshness、media、breaking news、category and personalization。
今日固定时间表
三个学习窗口必须保持 exactly 08:50-10:55, 14:30-16:15, 20:30-21:15。
| 08:50-09:20 | 08:50-10:55 system design Blind reattempt: how to show fresh articles within 30 minutes without per-request global ranking. |
|---|---|
| 09:20-10:05 | 08:50-10:55 system design Read all News deep dives and bonus deep dives using original heading anchors. |
| 10:05-10:35 | 08:50-10:55 system design Deep dive: cursor pagination, cache hierarchy, freshness pipeline, traffic spikes and recovery. |
| 10:35-10:55 | 08:50-10:55 system design DDIA Ch13 reprocessing/observability: monitor index lag and stale feed rows. |
| 14:30-16:15 | NeetCode Graphs Three contiguous Graphs slots below; no other tag. |
| 20:30-21:15 | Staff Q&A nodes 8-11; no Applied-AI radar because no first-party source changed decisions. |
算法模块
NeetCode Graphs, exactly three slots today, contiguous slots 10-12 of 21.
| # | Problem / mode | Pattern | Invariant | Bug risk | Time | Space |
|---|---|---|---|---|---|---|
| 10 | Rotting Oranges Graphs · NEW · 30m solve + 5m evidence | multi-source BFS | minute advances by BFS layers from all initial rotten cells | incrementing time per cell instead of per layer | O(mn) | O(mn) |
| 11 | Walls and Gates Graphs · NEW · 30m solve + 5m evidence | multi-source BFS distance | first time reaching a room is shortest distance to any gate | starting BFS from every room | O(mn) | O(mn) |
| 12 | Course Schedule Review Graphs · NEW · 30m solve + 5m evidence | cycle detection review | cycle in prerequisite graph makes schedule impossible | marking visited too early | O(V+E) | O(V+E) |
今日产出
| 必须交付 | News transfer final mapping and follow-up answer. |
|---|---|
| 修复规则 | If pagination uses offset over a moving feed, replace with score/time/id cursor and snapshot boundary. |
Hello Interview 精确目录
使用 live heading 的 original title 和 direct anchor。
| 项目 | Level | 精确 canonical section | Disposition | Day |
|---|---|---|---|---|
| News Aggregator / Google News | h2 | Potential Deep Dives | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 1) How can we improve pagination consistency and efficiency? | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 2) How do we achieve low latency (< 200ms) feed requests? | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 3) How do we ensure articles appear in feeds within 30 minutes of publication? | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 4) How do we handle media content (images/videos) efficiently? | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 5) How do we handle traffic spikes during breaking news? | transfer deep dive | Day 4 |
| News Aggregator / Google News | h2 | Bonus Deep Dives | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 6) How can we support category-based news feeds (Sports, Politics, Tech, etc.) | transfer deep dive | Day 4 |
| News Aggregator / Google News | h3 | 7) How do we generate personalized feeds based on user reading behavior and preferences | transfer deep dive | Day 4 |
DDIA 精确决策卡
Only DDIA Ch4 and Ch13 decision links are allowed.
| Day | Project | Decision | Link |
|---|---|---|---|
| Day 4 | News Aggregator | freshness SLO requires observing index lag and stale derived state | https://ddia.vonng.com/ch13/#sec_future_observing |
| Day 4 | News Aggregator | schema/ranking evolution needs reprocessing rather than hand edits | https://ddia.vonng.com/ch13/#sec_future_reprocessing |
Artifacts
PDF is intentionally absent; Week 9 requires MP3 only for the FULL/TRANSFER scripts.
Detailed lecture notes, audio, recall scripts, PDFs, Staff Q&A, and mock packs are archived locally and are intentionally not published on this site.