Four people, four hats and a wall in between. Every silence in this problem says as much as an answer, and following the thread of what each prisoner can or cannot see is the only way to get to the end.
The four prisoners and the wall
Riddle statement
Four prisoners—A, B, C, and D—are lined up, in that order. A wall separates C from D, so that no one looks at the other side.
- A sees B and C.
- B sees C.
- C and D do not see any other prisoners.
Exactly four hats are distributed: two black and two white, one per prisoner. They all know that distribution.
They are asked, one by one, if they can deduce the color of their own hat. After a few moments, one of them answers yes.
Who is he, and how do you know?