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This question already has an answer here:

Picture this.

You are in a hallway of a very large office building.

Near you are 50 light switches of which 3 are unlabled. These lightswitches are connected to 3 lights in 3 separate rooms. The rooms are not directly in your line of sight as there are 47 other rooms too.

This makes it that walking up and down from the lightswitches to the rooms a tedious task that you want to avoid. Because the other 47 lightswitches do have lables, you do know which 3 of the 50 rooms have yet to be labled.

Your task is to efficiently find out which lightswitch is connected to which room.

To give an idea of the challenge, it means that you walk from the lightswitches to the 3 rooms then back and know which switch is connected to which room so you can label them.

How would you proceed?

I do know the answer, but will refrain of answering my own question unless everyone gives up.

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marked as duplicate by klm123, Kendall Frey, kaine, Joe Z., Aza Jul 26 '14 at 17:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ I believe this is a duplicate but can't access it right now. $\endgroup$ – kaine Jul 22 '14 at 23:29
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    $\begingroup$ @kaine: Were you perhaps thinking of puzzling.stackexchange.com/questions/27/… (found at the top of the "related questions" list in the side bar)? $\endgroup$ – Ilmari Karonen Jul 23 '14 at 1:20
  • $\begingroup$ How "efficient" are we talking? I can do it by flipping two switches and walking over, back, and over again (not all in that exact order), but I get the feeling you're looking for something even better. $\endgroup$ – Dennis Meng Jul 23 '14 at 3:26
  • $\begingroup$ @ilmarikaronen Yes (im on the android app so don't have that bar nor address bar) the only difference is if he implies it is too far to walk without the bulb cooling down. Otherwise it is identical (doing 3 bulbs instead of one the same way) $\endgroup$ – kaine Jul 23 '14 at 3:30
  • $\begingroup$ I completely missed the related question, but yes its identical. The idea is to power one on for a longer time and turn it off before you walk to the rooms so you can feel its still warm. $\endgroup$ – LPChip Jul 23 '14 at 7:29
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  1. On first switch among the three and keep it on for 10 mins.
  2. Off the first switch and on the second switch.
  3. Now proceed towards the room.
  4. The room in which light bulb is hot (you need to touch the light bulb) belongs to first switch
  5. The room in which light bulb is on belongs to second switch which we have left on before coming towards rooms.
  6. The room in which light is not on belongs to third switch, which we have not switched on yet.
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