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System design

附近的人 / 打车派单

这其实是两道题,很多人把它们混成一道。

Copy the prompt, then pick a model. It plays the interviewer and asks you through it scene by scene instead of handing you the answer.

On a phone with the app installed, the system opens the app directly. Links cannot open external apps inside WeChat — open it in a browser first.

The copied text ends with the answer key the model grades you against. Don't read it yourself first — working it out on your own is the point.

「找出附近的人」是索引问题,「派给谁」是匹配问题。混成一道,正是这题要考的。

索引那半的必答点在边界和密度差异上 —— 网格切好之后,人不会均匀地站在格子里。

★★★★☆ · about 40 min · Tests: GeoHash 的边界问题、密度差异、高频位置上报、批量撮合 vs 来一单派一单

Cross-cutting patterns this one leans on

Hotspots and data skew Caching State machines and timeout compensation Idempotency Sharding and distributed IDs Observability

Have you done this one?

Sign in to mark this one as practised — next time you come back you'll see when you did it.

Notes from people who did this one

Nobody has written yet. After you run it, say what came out of the conversation — which scene stumped you, which conclusion you changed afterwards.

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How to use this

How to start

  1. Pick a question, open it, copy the prompt.
  2. Paste it into a brand-new conversation — not one where you already discussed this question, or the model follows your old answers.
  3. Say nothing. Wait for its first question.

Four commands you can call out at any time

  • 跳过 move to the next scene now
  • 提示 give a direction, not the answer
  • 直说吧 spell this point out in full, then keep pressing on the trade-offs
  • 复盘 jump to the wrap-up and print the review card

Three traps

  • Don't do two questions in one conversation — context from the first makes the model prejudge your level.
  • Don't look up the answer the moment it asks. Being stuck for 30 seconds is itself useful information.
  • When it starts praising you, point it back to rule five — feeling validated crowds out noticing what you missed.

Suggested order: start with the cross-cutting drill as a parts test, use the short-link question to get used to the flow, then pick by the direction you interview for, and keep redoing the one about your own project.