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Topic: Three Locks (Read 801 times) |
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Nerde
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Three Locks
« on: Mar 30th, 2003, 10:14am » |
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Here, each theif will select 2 locks at random and toggle them. He will then inform the next theif such that at the end
each one knows about the sequence exactly one other theif.
Then, when 2 get together its just about making sure each
lock is toggles twice.
Howz it!!
Nerd
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steveo
Newbie
Posts: 1
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Re: Three Locks
« Reply #1 on: Apr 2nd, 2003, 8:13am » |
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The 1st criminal picks activate/deactivate states for the 3 locks and tells the 2nd. The 2nd does the same and tells the 3rd. The 3rd tells the 1st.
So,
#1 knows 1,3
#2 knows 1,2
#3 knows 2,3
Any combination of 2 prisoners has all 3 on/off states and no one has all 3. To determine which locks are activated, 2 prisoners get together and XOR (Exclusive OR) the 3 states.
e.g.
#1 set locks 1,0,1
#2 set locks 1,0,0
#3 set locks 0,1,1
-----------------
XOR result 0,1,0
In this case only the 2nd lock is activated. Toggle it off and open the door.
steveo
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aero_guy
Senior Riddler
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Posts: 513
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Re: Three Locks
« Reply #2 on: Apr 2nd, 2003, 11:53am » |
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Original post: here
Be sure to search, welcome to the board.
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