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wu :: forums    riddles    hard (Moderators: SMQ, Eigenray, towr, Grimbal, Icarus, ThudnBlunder, william wu)    Hard- Fork problem « Previous topic | Next topic » Pages: 1  Reply Notify of replies Send Topic Print    Author  Topic: Hard- Fork problem  (Read 2500 times) Cze-Jwin Guest Hard- Fork problem   « on: Jul 24th, 2002, 2:55am » Quote Modify Remove the question to ask is..   what would your brother say is the correct path?   path a = wrong path path b = correct path brother 1 = always truth brother 2 = always lies   if you asked brother 1, the answer would be path b   if you asked brother 2. the answer would also be path b because brother 1 will say that path a is the correct one, to lie he has to say taht brother 1 will say path b IP Logged knox Guest Re: Hard- Fork problem   « Reply #1 on: Jul 25th, 2002, 5:26am » Quote Modify Remove Cze-Jwin I think the question is correct, but you headed in the wrong direction.   brother 1 (nice) knows his brother lies and will tell you the wrong path. brother 2  (mean) knows his brother would give you the right way, to lie he will tell you the wrong path.   So the answer you get from both is the _wrong_ path. Have fun at the cannibals.   IP Logged Matt S Guest Re: Hard- Fork problem   « Reply #2 on: Jul 25th, 2002, 10:52am » Quote Modify Remove knox has it correct. Actually, CZE-Jwin had the the right question to ask, but his analysis was incorrect.     The solution: Ask the question -- "What would your brother say is the correct path?"   THEN take the OPPOSITE of whatever he says, since the answer given will be the path to the cannibals.         IP Logged drdedos Guest Re: Hard- Fork problem   « Reply #3 on: Jul 25th, 2002, 4:07pm » Quote Modify Remove Another question that would work is if i pointed to a path and asked, "If i asked you if that was the correct path, would you say yes?"   If the path I pointed to was the correct path, - the truth-sayer would say "yes" - the liar would lie and say "yes," since if i did ask him if it was the correct path, he would lie and say "no."   If the path I pointed to was the wrong path, - the truth-sayer would say "no" - the liar would lie and say "no," since if i did ask him if it was the correct path he would lie and say "yes."   Either way, you would know if the path you pointed to was correct or not, and can proceed as you wish. IP Logged Cze-Jwin Guest Re: Hard- Fork problem   « Reply #4 on: Jul 25th, 2002, 5:42pm » Quote Modify Remove hahah so i fergot to mention that you need to take the opposite path... IP Logged greg Guest Re: Hard- Fork problem   « Reply #5 on: Jul 25th, 2002, 7:20pm » Quote Modify Remove Why not ask him how many fingers your holding up, or what color the sky is? IP Logged greg Guest Re: Hard- Fork problem   « Reply #6 on: Jul 25th, 2002, 7:26pm » Quote Modify Remove or ask one of them if he has a brother. IP Logged DocBot Newbie     Gender: Posts: 2 Re: Hard- Fork problem   « Reply #7 on: Jul 26th, 2002, 8:52am » Quote Modify ...well, that wouldn't really help you choose a path, now would it?   IP Logged neo Guest Re: Hard- Fork problem   « Reply #8 on: Jul 26th, 2002, 10:57am » Quote Modify Remove Ask any of them ; "which path goes to your hometown?"     that's all ) IP Logged Gamer555 Newbie     Posts: 19 Re: Hard- Fork problem   « Reply #9 on: Jul 30th, 2002, 9:40am » Quote Modify Good job neo, that is another good solution. IP Logged Peter Newbie     Gender: Posts: 3 Re: Hard- Fork problem   « Reply #10 on: Jul 30th, 2002, 3:09pm » Quote Modify I can't see that neo's answer helps despite Gamer555's plaudits.     I've seen Cze-Jwin's answer before (many years ago, regretably) where you ensure you get a lie and act in that knowledge but I really like drdedos' answer where you force the liar to tell the truth ... well almost!   The real purpose of this note is to ask "what is the difference between fork problem #1 and fork problem #2?", have all angles been covered in the discussion above or is there, as is implied in the questions, a simpler answer to number 1? IP Logged smst Newbie     Posts: 2 Re: Hard- Fork problem   « Reply #11 on: Aug 2nd, 2002, 1:08am » Quote Modify on Jul 30th, 2002, 3:09pm, Peter wrote: I can't see that neo's answer helps despite Gamer555's plaudits.     I've seen Cze-Jwin's answer before (many years ago, regretably) where you ensure you get a lie and act in that knowledge but I really like drdedos' answer where you force the liar to tell the truth ... well almost!   The real purpose of this note is to ask "what is the difference between fork problem #1 and fork problem #2?", have all angles been covered in the discussion above or is there, as is implied in the questions, a simpler answer to number 1? There is a difference, and that difference is such that neo's answer will work for the first question (hence Gamer555's response).  The crucial difference is that in the first problem, you know that the liar comes from the village of cannibals and that the truth-teller comes from the village of safety. Hence asking either one the direction to their own village will give you the necessary information: The truth-teller will point you at his own village (which is where you want to go). The liar will not point to his own village, but will lie and point to the village of safety. Either way, they point at the correct path.   In the second problem the information linking individuals to villages is not given -- this lack of information makes the  problem harder (as you rightly point out, neo's solution won't work in this case). I suspect that, even if we knew from which village the twins came, the problem would still require the indirect-question answer given above, since the simple "where are you from?" will yield different answers (because the truth in each case is the same village, so each twin will point to a different one). IP Logged Darkstar Guest Re: Hard- Fork problem   « Reply #12 on: Aug 26th, 2002, 4:35pm » Quote Modify Remove Hehe... anyone seen "Into the Labyrinth"? The movie with David Bowie and Jennifer Connelly? That's where I knew the answer from   --Darkstar IP Logged James Fingas Uberpuzzler     Gender: Posts: 949 Re: Hard- Fork problem   « Reply #13 on: Aug 29th, 2002, 6:43am » Quote Modify "Where are you from?" IP Logged Doc, I'm addicted to advice! What should I do? arvind mayank Guest Re: Hard- Fork problem   « Reply #14 on: Oct 13th, 2002, 2:13pm » Quote Modify Remove what if there is only one brother (one person) and dont know that whether he always tells truth or lies.now whats the single question u gonna ask that person to know the correct path.   reply soon IP Logged arvind mayank Guest Re: Hard- Fork problem   « Reply #15 on: Oct 13th, 2002, 2:15pm » Quote Modify Remove what if there is only one brother (one person) and u dont know that whether he always tells truth or lies.now whats the single question u gonna ask that person to know the correct path.   reply soon IP Logged TimMann Senior Riddler     Gender: Posts: 330 Re: Hard- Fork problem   « Reply #16 on: Oct 13th, 2002, 6:24pm » Quote Modify on Oct 13th, 2002, 2:15pm, arvind mayank wrote: what if there is only one brother (one person) and u dont know that whether he always tells truth or lies.now whats the single question u gonna ask that person to know the correct path.   reply soon   dredos replied to that one before you asked it. See reply #3 above. How's that for "soon"?   IP Logged http://tim-mann.org/ Pages: 1  Reply Notify of replies Send Topic Print Forum Jump: ----------------------------- riddles -----------------------------  - easy   - medium => hard   - what am i   - what happened   - microsoft   - cs   - putnam exam (pure math)   - suggestions, help, and FAQ   - general problem-solving / chatting / whatever ----------------------------- general -----------------------------  - guestbook   - truth   - complex analysis   - wanted   - psychology   - chinese « Previous topic | Next topic »

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