今日固定时间表
三块窗口固定：08:50-10:55 系统设计，14:30-16:15 算法，20:30-21:15 口述。
| 08:50-09:20 | 08:50-10:55 system design 25-35 分钟 attempt - 闭卷设计 create auction、place bid、view auction；先声明 close rule 和 tie-break。 |
|---|---|
| 09:20-09:50 | 08:50-10:55 system design 精确原文 - 读 Online Auction required anchors 到 HLD 三条用户路径。 |
| 09:50-10:25 | 08:50-10:55 system design 白板主路径 - POST bid -> per-auction ordered append -> validate > highest -> accepted/rejected -> broadcast current highest。 |
| 10:25-10:55 | 08:50-10:55 system design DDIA 决策卡 - 用 lost update 解释 stale max-bid 失败，写出 duplicate bidId retry 的返回语义。 |
| 14:30-16:15 | NeetCode Tag · Binary Search 三道题，每题 30m solve + 5m evidence，不能改 tag。 |
| 20:30-21:15 | 20:30-21:15 Online Auction English recall outline + 8 分钟 follow-up：同金额和截止前后 bid。 |
算法模块
连续 NeetCode Binary Search；每天 exactly 3 slots。
| # | Problem / mode | Pattern | Invariant | Bug risk | Time | Space |
|---|---|---|---|---|---|---|
| 1 | Missing Number In Arithmetic Progression NEW · 30m solve + 5m evidence | expected-value predicate | Before missing point, arr[i] equals arr[0] + i*d. | Wrong diff sign or using endpoints when length is tiny. | O(log n) | O(1) |
| 2 | Check If a Number Is Majority Element in a Sorted Array NEW · 30m solve + 5m evidence | lower/upper bound count | The sorted range for target is contiguous. | Inclusive/exclusive count mistakes when target absent. | O(log n) | O(1) |
| 3 | Missing Element in Sorted Array NEW · 30m solve + 5m evidence | missing-count predicate | missing(i) is monotonic by index. | Confusing kth missing before array with inside-array count. | O(log n) | O(1) |
Hello Interview 精确目录
保留 live canonical heading title；day page 使用 direct section anchors。
| 项目 | 精确 canonical section | Disposition | 今天怎么用 |
|---|---|---|---|
| Online Auction | Understanding the Problem | required reading | auction item, bids, closing rule and winner |
| Online Auction | Functional Requirements | required reading | post auction, bid, view auction and current highest bid |
| Online Auction | Non-Functional Requirements | required reading | strong consistency for bids, durability, real-time display, 10M auctions |
| Online Auction | The Set Up | required reading | scope and framework entry |
| Online Auction | Defining the Core Entities | required reading | Auction, Item, Bid, User |
| Online Auction | API or System Interface | required reading | create auction, place bid, view auction |
| Online Auction | High-Level Design | required reading | auction service, bidding service, current bid read path |
| Online Auction | 1) Users should be able to post an item for auction with a starting price and end date. | required reading | seller creates auction and item |
| Online Auction | 2) Users should be able to bid on an item. Where bids are accepted if they are higher than the current highest bid. | required reading | bid validation and accepted/rejected status |
| Online Auction | 3) Users should be able to view an auction, including the current highest bid. | required reading | view state and real-time highest bid |
DDIA 精确决策卡
只使用 Ch8 和 Ch10 中直接解决今天设计决定的小节。
| 项目 | 项目问题 | 精确 DDIA subsection | 改变的系统决定 |
|---|---|---|---|
| Online Auction | Why can two stale bidders both appear accepted, and how is that prevented? | Ch8 - 防止丢失更新 | Bid acceptance reads and updates current_highest_bid under one isolation boundary or conditional versioned update. |
三域 trace 任务
Winning transaction标出唯一线性化点：seat hold/sold、accepted bid at close、brokerage order/execution state。
Duplicate/retry failure给出 stable idempotency key、重复返回语义、旧 owner/stale version 被拒绝的证据。
Projection boundary说明哪些读可以陈旧：seat map、highest bid display、market price UI；哪些写不能陈旧。
本日 artifacts
项目脚本、音频、PDF 和 mock evidence 从当天直接打开。
今日产出、修复与英语 recall
| 课程角色 | FULL · original reading + 30m attempt |
|---|---|
| 必须交付 | Online Auction 30m attempt + HLD：Auction/Item/Bid/User、bid status、highest bid projection、winning bid trace。 |
| 修复规则 | 如果只保存 maxBid 而丢 bid history，重写 append-only ledger 和 audit dispute path。 |
| English recall | English recall: Bids are facts; current highest bid is a projection with a strict acceptance rule. |
Detailed lecture notes, audio, recall scripts, PDFs, Staff Q&A, and mock packs are archived locally and are intentionally not published on this site.