Observe the world
System design sparring
Prompts you copy and take elsewhere. Paste one into any large model and it plays the interviewer, asking you through the problem scene by scene rather than reciting the answer.
These prompts only exist in 简体中文 for now.
How to use this
How to start
- Pick a question, open it, copy the prompt.
- Paste it into a brand-new conversation — not one where you already discussed this question, or the model follows your old answers.
- 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.
Frequently asked
秒杀 / 限时抢购
一秒钟涌进来十万个人，只有一百件货。
支付系统
钱不能多也不能少，而第三方随时超时。
订单与库存（电商交易链路）
一条链路跨四个服务，中间任何一步都可能失败。
短链系统
最简单的一道，专门考基本功。
Feed 流 / 朋友圈 / 微博时间线
读扩散还是写扩散，以及那个有一千万粉丝的人。
IM / 即时通讯
消息不能丢、不能重，还要在三个端上一致。
排行榜 / 计数系统
ZSet 谁都会用，同分怎么排、亿级怎么算名次就不一定了。
优惠券 / 红包
发一亿张券，核销不能重复，拆红包不能多出一分钱。
通知与推送系统
多通道、有配额，还不能把同一条推两遍。
限流器
四种算法的临界问题，以及计数的那台 Redis 挂了你放还是不放。
大文件上传 / 网盘
分片、续传、秒传，以及回调凭什么可信。
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。
定时任务调度系统
只执行一次，以及「该跑没跑」怎么发现。
评论 / 树形结构
三种树存储没有绝对优劣，所以得先问产品要什么。
Special drills
通用模板：任何一道系统设计题
索引里没有的题，套这一份。
横切套路：第二层追问快问快答
专治「结论会背、推导讲不出」。
讲自己的项目
把「我做过一个 XX 系统」逼成三个数字 + 一个取舍 + 一个故障。