# [plt-scheme] Effect of caching using hash-tables vs vectors

 From: jos koot (jos.koot at telefonica.net) Date: Sun Mar 18 08:16:51 EDT 2007 Previous message: [plt-scheme] Effect of caching using hash-tables vs vectors Next message: [plt-scheme] Effect of caching using hash-tables vs vectors Messages sorted by: [date] [thread] [subject] [author]

```Hi Eli,
I am interested in how you solved the problem using a vector while not knowing beforehand the maximum number that will be generated while cycling.
Jos koot

(((((lambda(x)((((((((x x)x)x)x)x)x)x)x))
(lambda(x)(lambda(y)(x(x y)))))
(lambda(x)(x)x))
(lambda()(printf "Greetings, Jos~n"))))
----- Original Message -----
From: Eli Barzilay
To: Daniel Yoo
Cc: plt-scheme at list.cs.brown.edu
Sent: Saturday, March 17, 2007 9:34 PM
Subject: Re: [plt-scheme] Effect of caching using hash-tables vs vectors

On Mar 17, Daniel Yoo wrote:
> Just for fun, I did a solution for the 3n+1 problem from Programming
> Challenges:
>
>      http://acm.uva.es/p/v1/100.html
> [...]

Unrelated to your post -- but I played with this a while ago.  I
eventually realized that there are certain bit patterns that need to
be checked in a specific way, and ended up writing Scheme code that
would generate C code for each of these tests, then run it.  I managed
to prove that the thing converges up to something in the neighborhood
of numbers that are known to converge.  (I think it was something
around 1e20.)  I can send you the file if you're interested -- but it
will take some time to decipher what it's doing.
--
((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
http://www.barzilay.org/                 Maze is Life!
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