GS Chandy
Posts:
7,941
From:
Hyderabad, Mumbai/Bangalore, India
Registered:
9/29/05


Re: Please help me with the following question
Posted:
Mar 8, 2013 2:08 AM


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 'Bruteforce' search:   https://en.wikipedia.org/wiki/Bruteforce_search   http://www.algorithmist.com/index.php/Exhaustive_Search   http://wwwrci.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 '12ball' or '12coin' withthreeweighings problem:
It certainly IS a problem that does require (a very little) 'outofthebox' 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 'outofthebox' 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

