Combinatorics algorithm

[all_my_trash@hotmail.com]

Hello!

I'm trying to write an algorithm which can fill an array with all the
possible combinations of r out of n, without repetition (maximum
combinations = n!/(r!(n-r)!))

However, my mathematical skills are insufficient - does anybody have
such an algorithm for sharing?

Regards,
OMykle

[Craig Storey]

Re: Combinatorics algorithm

all_my_trash@ho tmail.com wrote:

Hello!
>
I'm trying to write an algorithm which can fill an array with all the
possible combinations of r out of n, without repetition (maximum
combinations = n!/(r!(n-r)!))
>
However, my mathematical skills are insufficient - does anybody have
such an algorithm for sharing?
>
Regards,
OMykle
>

Hopefully this isn't for homework...but if it is then you are copying
mine. :) This is untested code, but mathematically correct. For bonus
marks you can figure out how to do this recursively.

function Factorial($x)
{
if ($x<1) {echo "Factorial( ) Error: Number too small!";)
$ans = 1;
for ($xx=2; $xx>=$x; $xx++)
{
$ans = $ans * $xx;
}
return($ans);
}

function Permutation($se lectcount,$avai lablecount)
{
$ans = Factorial($avai lablecount) /
Factorial($avai lablecount-$selectcount);
return ($ans);
}

function Combination($se lectcount,$avai lablecount)
{
$ans = Factorial($avai lablecount) / (
Factorial($avai lablecount-$selectcount) * Factorial($sele ctcount) );
return ($ans);
}

[zman]

Re: Combinatorics algorithm


all_my_trash@ho tmail.com wrote:

Hello!
>
I'm trying to write an algorithm which can fill an array with all the
possible combinations of r out of n, without repetition (maximum
combinations = n!/(r!(n-r)!))
>

Java code is given here (which will give you the psuedo code for php
code):

http://www.merriampark.com/comb.htm

zafar
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