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03-26-2011 , 10:58 AM

Gullanian

Carpal \'Tunnel

Join Date: Dec 2006 Posts: 14,014

I love prime numbers, and they have some amazing applications in cryptography as well as some other things.

This is a pretty useless application of primes, but it's a good demonstration I wrote to show off one of the amazing properties of prime numbers.

Given a word, work out if one word is a scrambled version of another. IE, boat and btoa is true, but bota and booat is false. Same number of characters, same characters.

Quote:

a=[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61, 67,71,73,79,83,89,97,101];
function b(c)
{
r=1;
for(i=0;i<c.length;i++)
r*=a[c[i].charCodeAt(0)-97];
return r
}

Then do:

Quote:

alert(b("hello")==b("elloh"));

(It's obfuscated a bit as it was for a competition, it's the least obfuscated one I've got)

Anyone else got any interesting prime number snippets or applications? I'd love to see them!

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03-26-2011 , 03:21 PM

well named

poorly undertitled

Join Date: Jun 2007 Posts: 78,077

Interesting. I think that algorithm is in principle similar to the numbering scheme invented by Godel

http://en.wikipedia.org/wiki/G%C3%B6del_numbering

Although in that case Godel was also interested in being able to deconstruct the numbered elements.

In any case, yay prime numbers?

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03-26-2011 , 04:40 PM

jukofyork

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Join Date: Sep 2004 Posts: 11,749

Not sure if you've seen this before: http://www.suffecool.net/poker/evaluator.html

Interesting poker-programming use of prime numbers.

Juk

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03-26-2011 , 05:22 PM

Gullanian

Carpal \'Tunnel

Join Date: Dec 2006 Posts: 14,014

Ah yes, juk, for my uni project I did something similar to that at used it as my main material. It made an interesting 2+2 let me see if i can find it

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03-26-2011 , 05:24 PM

Gullanian

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Join Date: Dec 2006 Posts: 14,014

LOL yeah one of my first posts!

http://forumserver.twoplustwo.com/45...valuators-597/

It's an interesting read if your into optimisations and stuff relating to poker.

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03-26-2011 , 06:55 PM

_dave_

_Pooh_Bah_

Join Date: Feb 2005 Posts: 13,146

"an interesting 2+2" is quite the understatement, that thread advanced the state of the art in hand evaluation by leaps and bounds IIRC! Still goes way over my head though!

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03-26-2011 , 07:55 PM

wellju

BSOD and racetrack Ninja

Join Date: Feb 2010 Posts: 5,247

Prime numbers can do quite cruel things to your mind imo, even tho they have some kind of magical beauty to them.

http://projecteuler.net/index.php?section=problems

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03-27-2011 , 03:37 AM

goofyballer

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Join Date: Jun 2005 Posts: 70,719

Quote:

Originally Posted by wellju

Prime numbers can do quite cruel things to your mind imo, even tho they have some kind of magical beauty to them.

http://projecteuler.net/index.php?section=problems

This link is entirely too much fun. I've gotten through 17 so far.

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03-27-2011 , 01:50 PM

jukofyork

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Join Date: Sep 2004 Posts: 11,749

Quote:

Originally Posted by Gullanian

LOL yeah one of my first posts!

http://forumserver.twoplustwo.com/45...valuators-597/

It's an interesting read if your into optimisations and stuff relating to poker.

Ah yeah, that was an awesome thread! Didn't realize it was you who started it.

Juk

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03-27-2011 , 08:16 PM

#10

RustyBrooks

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Join Date: Feb 2006 Posts: 24,647

That was a truly epic thread and I've probably read it top to bottom 4 or 5 times.

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03-31-2011 , 10:30 PM

#11

DrSayre

grinder

Join Date: Aug 2005 Posts: 676

Anybody want to form a team on GIMPS (http://mersenne.org/gettingstarted/)?

Last edited by jukofyork; 04-01-2011 at 08:43 AM. Reason: Fixed broken URL.

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04-05-2011 , 11:52 PM

#12

Johnny Douglas

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Join Date: Apr 2008 Posts: 8,480

Quote:

Originally Posted by Gullanian

Given a word, work out if one word is a scrambled version of another. IE, boat and btoa is true, but bota and booat is false. Same number of characters, same characters.

Nice. Same approach used in Cactus Kev's Pokerhand Evaluator

Quote

04-15-2011 , 08:12 PM

#13

Styhn

old hand

Join Date: Aug 2007 Posts: 1,270

I don't know if this is considered programming-related but here's an interesting way to generate a texture (wallpaper, background, whatever) which looks random but only takes a single tile and some mathemagicks to generate (using prime numbers, ofc).

http://designfestival.com/the-cicada...web-designers/

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04-15-2011 , 08:17 PM

#14

Johnny Douglas

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Join Date: Apr 2008 Posts: 8,480

Quote:

Originally Posted by Styhn

Great article, highly recommend it!

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