Give me one of those tricky microsoft-style interviev questions. The ones that are puzzles

2 upvotes

3 years and 10 months later

GPT-3.5

December 22, 2022

Sure! Here's a classic Microsoft-style interview question: You have 100 identical light bulbs arranged in a row. Each bulb has its own switch and is currently off. You are given the opportunity to flip the switch of any bulb at any time. However, you may only flip the switch of a given bulb once. The goal is to turn on all the light bulbs by flipping the switches in a sequence such that the final confiquration has all light bulbs on. What is the minimum number of switches you need to flip in order to achieve this goal? Hint: Think about the pattern of switches you would need to flip in order to turn on every other light bulb, and then every fourth light bulb, and so on.

GPT-6 Astra

October 19, 2026

Here’s a classic interview-style brain teaser:

You have two ropes and a lighter. Each rope takes exactly 60 minutes to burn completely, but they burn unevenly—half a rope might burn in 5 minutes and the other half in 55.

You can light either end of either rope, but you have no clock or other measuring tools.

How can you measure exactly 45 minutes?

ShowHide Astra's reasoning 63 words

Creating a tricky puzzle

I'm thinking about crafting a puzzle for the user with no solution to offer them a challenge. I could use three switches from a classic MS puzzle, but I won't specify any exact attribution. As for the heat source, I could clarify that the puzzle involves incandescent bulbs. Also, ropes could be an option—common and tricky, perhaps allowing a maximum time of 45 minutes. Just to note, no caveats for burning the ends since they burn at an irregular rate. I’ll provide two ropes, each lasting 60 minutes for the challenge.

What changed

GPT-3.5’s puzzle isn’t really a puzzle. If 100 bulbs start off and each switch can be flipped only once, the answer is obviously 100: flip every switch. The hint about “every other light bulb, and then every fourth” seems to be a garbled memory of the famous 100 lockers problem, where repeated passes leave only the perfect squares open. Here the setup and the hint don’t match, so a candidate would be left chasing a pattern that doesn’t exist.

Astra offers the classic rope-burning teaser, and it is stated cleanly. The key constraint is spelled out, that ropes burn “unevenly,” which rules out simply cutting one in half, and the question, “How can you measure exactly 45 minutes?”, is precise. It also holds back the solution, which suits someone who asked to be quizzed. The puzzle is famous enough that a seasoned interviewee might already know it, but it is a working puzzle, and GPT-3.5’s was not.

Analysis by Claude Opus 5.5, comparing the two answers above.