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Solutions to plane crash, lightbulb questions.

"you have 3 switches and 3 lightbulbs in separate rooms. you are allowed to play with the switches and then go into the room with the bulbs only once (i.e. you can't go back and play with the switches again). how can you tell which switch goes to which bulb?"

the first question is just a trick. the second one is an "aha!" some people may say the second one requires "thinking outside the box" but i say "phooey!" its no good for an interview. you want to ask questions that have a process to them, so even if the candidate knows the answer, they still have to explain the process or algorithm to you to demonstrate they understand it. programming questions, math questions, and puzzles are the best option.

Algorithm for solving the light bulb problem:

Step 1: Flip on the left light switch. Leave on for one minute.

Step 2: Flip off the left light switch, flip on the middle switch, and walk into the room.

The bulb that is hot, but unlit goes to the left switch, the bulb that is lit goes to the middle switch, and the bulb that is cool and unlit goes to the right switch.

So how is this not a process?

Josh Everist
Sunday, January 5, 2003

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