this post was submitted on 25 Dec 2025
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Programmer Humor
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Only works if it’s an incandescent light, but…
Flip one switch. Wait a few minutes. Flip it off.
Flip the second switch and go into the room.
If the light is on, it’s the switch you flipped most recently. If the light is off but warm, it was the first switch. If it’s off and cold, it’s the switch you didn’t touch.
LED and fluorescent lights get hot too, it just takes a bit longer.
Yeah like few hours longer. And if I'm asked that I'll force the interviewer to sit through until it gets warm
You don't have to narrate your solution in real time.
You can visit the room once, doesn't say you can't swap the bulb for a smart bulb and use your phone to figure it out when it enters pairing mode...