Jiaqi Guo's home

Jiaqi Guo's home

Because there are two bits, the switches can represent the numbers 0,1,2,3 in binary, and it is possible for each person to flip a switch and either change the parity of the number, or leave it unchanged. For instance one flip will take 0 to 2, or 0 to 1; 1 to 0 or 1 to 3; 2 to 0 or 2 to 3, etc. Try working out a protocol where each prisoner knows what to do when he finds a given parity for the first, second, third,.... time he enters the room.