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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