Re: [PHP] generate all permutations possible? (solved!)

[michael geary]

beautiful! This seems to do the trick. Thanks very much!

-michael

On Thursday, April 3, 2003, at 07:45 PM, Leif K-Brooks wrote:

Try this (minimal testing, un-optimized):
function permutations($letters,$num){
   $last = str_repeat($letters{0},$num);
   $result = array();
   while($last != str_repeat(lastchar($letters),$num)){
       $result[] = $last;
       $last = char_add($letters,$last,$num-1);
   }
   $result[] = $last;
   return $result;
}
function char_add($digits,$string,$char){
   if($string{$char} <> lastchar($digits)){
       $string{$char} = $digits{strpos($digits,$string{$char})+1};
       return $string;
   }else{
       $string = changeall($string,$digits{0},$char);
       return char_add($digits,$string,$char-1);
   }
}
function lastchar($string){
   return $string{strlen($string)-1};
}
function changeall($string,$char,$start = 0,$end = 0){
   if($end == 0) $end = strlen($string)-1;
   for($i=$start;$i<=$end;$i++){
       $string{$i} = $char;
   }
   return $string;
}
michael geary wrote:

Hi Folks,

I'm struggling with a permutation problem.

I want to take a set of characters (for example "012345678ABCDEF") 
and generate all permutations of length N, allowing characters to be 
repeated. For example, I could use this algorithm to generate all 
HTML hex colors by passing:

generatePermutations("012345678ABCDEF",6)

Granted, this example would output some 16,777,215 items, but it 
would be a handy thing.

Note that I could get these color values by running from 0 to FFFFFF 
in hex, but I am looking for something more general so I can play 
with anagrams, etc.

I have seen some algorithms that generate permutations, but I don't 
want all permutations of "012345678ABCDEF", I just want all 6-digit 
permutations.

I have searched all over for algorithms, and have beat my head 
against it, but it is just escaping me. Can anyone help?

thanks,

michael


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