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MathGroup Archive 2005

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Re: Finding Position in an ordered list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57753] Re: [mg57720] Finding Position in an ordered list
  • From: yehuda ben-shimol <bsyehuda at gmail.com>
  • Date: Tue, 7 Jun 2005 02:04:07 -0400 (EDT)
  • References: <200506060821.EAA12541@smc.vnet.net>
  • Reply-to: yehuda ben-shimol <bsyehuda at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

The immediate answer is to perform a binary search. This will result
with a complexity of O(Log[2,n]) (n being the length of the list) and
not O(n).
There is an implementation of a binary search algorithm in the
Combinatorica package
<< DiscreteMath`Combinatorica`
? BinarySearch

good luck
yehuda
On 6/6/05, janostothmeister at gmail.com <janostothmeister at gmail.com> wrote:
> I wonder if it is possible to use the knowledge
> that a list in which I am looking for the position
> of an element is ordered. I want a quicker solution then e.g.
> lis={ac,dmk,rfg,sty,zxxer}
> Position[lis,sty]
> 
> I am certainly interested in longer lists...
> 
> Thank you,
> 
> Janos
> 
> 
>


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