EXTRAORDINARY PRISON RIDDLE TO TEASE YOUR BRAIN 

Additional note to the solution: prisoners don't necessarily have to turn the light on during their first visit. If on their first visit the light is already on, they should remember to turn on the light later in one of their subsequent visits.

It is not stated in the premise that a prisoner will be able to visit more than once. It is setup in such a way that it seems the prisoners will only appear in the room once, then never go back.

So they can see the light from their cells. At first i thought they couldnt which is harder and got a solution for that too. Also, the prisoner has to be inside the room to say that all the prisoners have already been to the room, which can take ages because the guard picks the prisoner randomly, so they can wait forever for that special prisoner to go to the room. i suggest this : 1) The prisoners must count the days. 2) if a prisoner walks in the room for the first time : if (the light is off and its past 50 days he says the magic sentence) else ( if the light is on he switches it off or if the light is off he ignores it). 3) if a prisoner walks in the room another time, he turns the light on or leaves it on if it is already on. this should work even if they cant see the light from their cells and doesnt need only one person to be in the room to save the rest.

Ok...each prisoner may switch on and off the light. Each prisoner has to switch the light ON and OFF on their FIRST visit and ignore on any subsequent visits. The prisoners must keep a tally of every on/off switch. The prisoner that enters the room after the 49th on/off light should say it to ensure every prisoner is set free.

what if they forget how many times the prisoners have been to the room? HOHOHOHOHO THEY'RE SCREWED

Maybe what you mean is that 49 prisoners should turn the light on (when its off obviously) once, and only once for each prisoner. It doesn't necessarily has to be on their first visit. If on their first visit the light is already on, they should remember to turn on the light later in one of their subsequent visits. "...turn the light on when they get to the room for the first time and ignore it on their subsequent visits" I think you worded that wrong, just want to point that out.

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