WEEK 09 · 2026.09.21-09.27 · WRITER GATE
Day 1 - FB Post Search FULL: attempt, requirements and HLD
2026-09-21 · MON · 35 分钟闭卷设计 FB Post Search，然后用原文 anchors 修正实体、API、倒排索引和排序路径。
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。
| 08:50-09:25 | 08:50-10:55 system design FB Post Search 35-minute design attempt: requirements, entities, write path, read path, latency split. |
|---|---|
| 09:25-10:05 | 08:50-10:55 system design Read live headings through search and sort HLD; copy every missed requirement into the attempt repair. |
| 10:05-10:35 | 08:50-10:55 system design Whiteboard inverted index construction: tokenization, posting list, index document, visibility snapshot, refresh. |
| 10:35-10:55 | 08:50-10:55 system design DDIA Ch4 decision cards for full text and multi-column/indexed sort choices. |
| 14:30-16:15 | NeetCode Graphs Three contiguous Graphs slots below; no other tag. |
| 20:30-21:15 | English recall outline: explain source of truth vs search index, then say recall/rank/presentation latency separately. |
算法模块
NeetCode Graphs, exactly three slots today, contiguous slots 1-3 of 21.
| # | Problem / mode | Pattern | Invariant | Bug risk | Time | Space |
|---|---|---|---|---|---|---|
| 1 | Number of Islands Graphs · NEW · 30m solve + 5m evidence | DFS/BFS grid components | visited prevents recounting the same island | forgetting to mark before recursion/queue push | O(mn) | O(mn) |
| 2 | Max Area of Island Graphs · NEW · 30m solve + 5m evidence | DFS/BFS connected area | each land cell contributes exactly once to one component | mixing rows/cols or missing zero grid | O(mn) | O(mn) |
| 3 | Flood Fill Graphs · NEW · 30m solve + 5m evidence | source color expansion | only original-color reachable cells are recolored | newColor equals original causing infinite revisit | O(mn) | O(mn) |
今日产出
| 必须交付 | FB Post Search first-pass HLD plus full-reading anchor coverage through sorted search path. |
|---|---|
| 修复规则 | If the design sorts all matching posts at request time, rewrite it into bounded retrieval plus rank. |
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 |
|---|---|---|---|---|
| FB Post Search | h2 | Understanding the Problem | required reading | Day 1 |
| FB Post Search | h3 | Functional Requirements | required reading | Day 1 |
| FB Post Search | h3 | Non-Functional Requirements | required reading | Day 1 |
| FB Post Search | h2 | Scale estimations | required reading | Day 1 |
| FB Post Search | h2 | The Set Up | required reading | Day 1 |
| FB Post Search | h3 | Planning the Approach | required reading | Day 1 |
| FB Post Search | h3 | Defining the Core Entities | required reading | Day 1 |
| FB Post Search | h3 | API or System Interface | required reading | Day 1 |
| FB Post Search | h2 | High-Level Design | required reading | Day 1 |
| FB Post Search | h3 | 1) Users should be able to create and like posts. | required reading | Day 1 |
| FB Post Search | h3 | 2) Users should be able to search posts by keyword. | required reading | Day 1 |
| FB Post Search | h5 | Approach | required reading | Day 1 |
| FB Post Search | h5 | Challenges | required reading | Day 1 |
| FB Post Search | h5 | Approach | required reading | Day 1 |
| FB Post Search | h5 | Challenges | required reading | Day 1 |
| FB Post Search | h3 | 3) Users should be able to get search results sorted by recency or like count. | required reading | Day 1 |
DDIA 精确决策卡
Only DDIA Ch4 and Ch13 decision links are allowed.
| Day | Project | Decision | Link |
|---|---|---|---|
| Day 1 | FB Post Search | keyword search is an inverted index, not SQL LIKE | https://ddia.vonng.com/ch4/#sec_storage_full_text |
| Day 1 | FB Post Search | recency and like sort need index/ranker fields, not presentation sorting | https://ddia.vonng.com/ch4/#sec_storage_index_multicolumn |
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.