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Op doesn't have time for interviews
(programming.dev)
Post:
You have three switches in one room and a single light bulb in another room. You are allowed to visit the room with the light bulb only once. How do you figure out which switch controls the bulb? Write your answer in the comments before looking at other answers.
Comment:
If this were an interview question, the correct response would be "Do you have any relevant questions for me? Because have a long list of things that more deserving of my precious time than to think about this!
If you don't know whether it's heavier or lighter, after the first test shows uneven you still have 6 coins possible. You can do it in 3 tests only if you know lighter vs heavier for the fake coin.
YOU'RE DOOMED! You must weigh two against two in the first step.