: Prisoner Puzzle v1.0 : the solution : Each prisoner except one, which we will call the ring-leader, turns the light on if : it was off. If it was on already, they leave it on. However, they turn the light on : exactly once - the first time they take a shower in which the light-switch was off. : The ring-leader is the only person who does something different. If she finds the : light on, she increments her counter and turns the light off. If she finds the light off, : she leaves it in that position. : In this manner, each other prisoner communicates a single bit of information to : the ring-leader, i.e. their having had their first shower. If the ring-leader's : counter ever reaches 'n', then she knows that all 'n' prisoners (including herself) : have had at least one shower and can make this assertion to the Warden, setting : them all free. : Prisoner Puzzle v2.0 : the set-up : Suppose now that the Warden sets the prisoners an even more difficult task. In order : to be freed, all of the prisoners must make the assertion that they have all had at : least one shower. This is a significantly harder problem; one which I don't know of : a solution for. : Good luck!