GS Chandy
Posts:
4,437
From:
Hyderabad, Mumbai/Bangalore, India
Registered:
9/29/05
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Re: Please help me with the following question
Posted:
Mar 8, 2013 2:08 AM
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Robert Hansen (RH) posted Mar 8, 2013 7:40 AM:
> That is a very hard problem. I managed to figure out
> weighings 1 and 3 but could not complete that middle
> step. This is not a binary search, it is an
> exhaustive search.
>
> Bob Hansen
>
That is NOT a "very hard problem" (See below the 'links' to 'binary' and 'exhaustive' searches, for the way I would rather describe it).
It is neither "a binary search" nor an "exhaustive search" (as you claim).
Some links about 'searches':
+++
'Binary search':
- -- https://en.wikipedia.org/wiki/Binary_search_algorithm
- -- http://community.topcoder.com/tc?module=Static&d1=tutorials&d2=binarySearch
- -- http://algorithms.openmymind.net/search/binarysearch.html
'Exhaustive' search (or 'Brute-force' search:
- -- https://en.wikipedia.org/wiki/Brute-force_search
- -- http://www.algorithmist.com/index.php/Exhaustive_Search
- -- http://www-rci.rutgers.edu/~cfs/472_html/AI_SEARCH/ExhaustiveSearch.html
(I've not studied - nor even read through - the material at those links - but they do not seem, at the barest glance, to be incompetent).
+++
Back to the '12-ball' or '12-coin' with-three-weighings problem:
It certainly IS a problem that does require (a very little) 'out-of-the-box' thinking to solve (an 'open mind', so to speak).
Joe Niederberger had been able to solve it when he was about 10 years old. I recall I had been able to solve it when I was around 10 or 11 years old - and it was the very first time I ever had an "EUREKA!" moment.
>From your description about 1st weighing,3rd weighing, etc - I believe you have not solved it yet.
For 'out-of-the-box' thinking, the OPMS approach could be quite useful, assuming one has an 'open mind' to begin with - and one is willing to look at and try to understand 'structural models' based on the "CONTRIBUTES TO" and "HINDERS" relationships.
GSC
("Still Shoveling!")
Joe Niederberger's post is pasted below.
> On Mar 7, 2013, at 4:35 PM, Joe Niederberger
> <niederberger@comcast.net> wrote:
>
> > By the way, the twelve coin problem is a real
> classic -- my father told me it when I was about 10.
> > Its easy enough to find a solution using Google,
> but as a courtesy to those who want to tough it out -
> please don't post a real solution here without the
> word "SPOILER" up front!
> >
> > Cheers,
> > Joe N
Message was edited by: GS Chandy
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