Lights and Switches

Problem: Four lights in a room and four switches outside the room that control the light. You can only enter the room to check if the lights are on. If you are outside, you don't know. How to know the mapping from switches to lights by just entering the room once?

Solution: The key is to find two binary classifier, then we can encode 4 lights. One classifier is On/Off. The other is Cold/Hot. So we can turn on two switches for a while, let the lights become hot. Then turn off one of them. Then turn on one of the the rest two switches.Then rush into the room to check. There must be four different statuses: On and Hot, Off and Hot, On and Cold, Off and Cold.