Interview Bank

Prompt Engineering From Scratch in 5 Days

D2 Few-Shot, Chain of Thought, Step-by-Step, and Self-Checks; When None of These Work

• Where does chain-of-thought prompting help most, where is it a waste, and how does it differ from splitting a task into steps?思维链在什么任务上提升明显，在什么任务上是浪费？它和「分步」有什么区别？

  Common in ChinaCommon overseasIntermediate#chain-of-thought#prompt-techniques

  How to reason about it · think before answering

  1. The discriminators are 'waste' and 'difference'. Anyone can say thinking first helps; the interviewer wants to hear when you deliberately skip it.
  2. Its value comes from intermediate results checking the next step, so it shines on multi-step reasoning, arithmetic and judgments with distractors; on single-step tasks such as classification, extraction or format conversion it adds latency, cost and length with little gain.
  3. Difference: chain-of-thought keeps everything in one call and one output budget; splitting uses several calls, each with its own budget and format, and later steps can consume earlier outputs. Use CoT when the model thinks too shallowly, split when one answer cannot hold the work.
  4. Conclusion: ask whether the task needs multi-step reasoning at all; if yes, ask whether one output can hold it — CoT if so, split if not.
  5. Follow-ups: with reasoning models that think internally, do you still write 'think step by step'? Usually no, but you still pin the answer format and position. And can you trust the written reasoning? It is a plausible narrative, not the actual computation — use it as a check, not as proof.

  分析过程 · 先想清楚再作答

  1. 题眼在「浪费」和「区别」。只会说「让模型先思考再回答效果更好」的候选人没有算过账，面试官想听的是你什么时候会主动不用它。
  2. 拆法：思维链的价值来自「中间结果可以校验下一步」，所以它在多步推理、算术、需要排除干扰项的判断上提升明显；在单步判断（分类、抽取、格式转换）上几乎没有增益，只有更慢更贵更长的输出。
  3. 区别：思维链是一次调用内让模型写出中间过程，输出预算还是同一份；分步是拆成多次调用，每步有独立的预算、独立的格式、并且后一步可以拿前一步的输出做输入。任务是「想得不够细」用思维链，任务是「一次装不下」用分步。
  4. 结论：先问任务是否需要多步推理，不需要就不用；需要的话再问一次输出装不装得下，装得下用思维链，装不下拆步。
  5. 追问：推理类模型内置了思考过程，还要写思维链吗？多数情况不用再写「一步步想」，但仍要指定最终答案的格式与位置，否则解析会很痛苦；另一个追问是思维链的内容能不能信，答案是它是「看起来合理的过程」而非真实的内部计算，只能当辅助校验不能当证据。

  Key points

  • CoT helps because intermediate results check the next step; strong on multi-step reasoning and arithmetic, wasted on single-step judgments
  • Cost is longer output, higher latency and spend, so skip it when no reasoning is needed
  • Versus splitting: CoT stays in one call with one budget; splitting uses multiple calls with independent budgets that can chain outputs
  • With reasoning models you rarely need 'think step by step' but still pin the answer format and location

  答题要点

  • 思维链的价值是中间结果校验下一步，多步推理与算术上提升明显，单步判断上是浪费
  • 代价是更长的输出、更高的延迟与费用，所以不需要推理的任务要主动不用
  • 与分步的区别：思维链是一次调用内写过程，输出预算不变；分步是多次调用，每步独立预算且可传递输出
  • 推理模型内置思考后一般不必再写「一步步想」，但仍要指定答案格式与位置