Kacam.net

System design

IM / 即时通讯

消息不能丢、不能重,还要在三个端上一致。

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.

长连接和 ACK 链是骨架,多端同步是分水岭 —— 能把同步模型讲清楚的人不多。

建议排在 Feed 之后做。

★★★★★ · about 50 min · Tests: 长连接管理、可靠投递的 ACK 链、seq 同步模型、多端一致、大群扩散

Cross-cutting patterns this one leans on

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

Have you done this one?

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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.