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.