[BITList] THE DOOR

[x50type at cox.net]

you mean like this, Hugh..............?


In the central prison of Sikinia there are n cells numbered 1 to n, each occupied by a single prisoner. The state of each cell can be changed from closed to open and vice versa by a half-turn of the key. To celebrate the Centennial Anniversary of the Republic it was decided to grant a partional amnesty. The president sent an officer to the prison with the instruction: 

for i:=1 to n do
  turn the keys of cells i, 2i, 3i, ... .

A prisoner was freed if at the end his door was open. Which prisoners are set free? Remark: Do not think, just sieve!



ct



From: HUGH 
Sent: Saturday, February 02, 2013 1:53 PM
To: BitList 
Subject: Re: [BITList] THE DOOR

Colin,

I sent a dissection of this trick a few years back, whether to BITlist or to BIShip I can't recall. It's a disguised sieve.

Hugh.


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