Logical algorithm to generate paths - algorithm

Question

I'm trying to develop an algorithm to create a symfony template service.
I want to check if a template exists in a subset of paths, ordered.
Given an array of parameter like this (already ordered like I want):
$params = ['O', 'U', 'W', 'P']
How can I output this array?
$urls = [
'O/U/W/P/template',
'O/U/W/template',
'O/U/P/template',
'O/U/template',
'O/W/P/template',
'O/W/template',
'O/P/template',
'O/template',
'U/W/P/template',
'U/W/template',
'U/P/template',
'U/template',
'W/P/template',
'W/template',
'P/template',
'template'
];
I can perform for a little list of parameters (like everyone can do it I suppose) with a code like this :
private function getPaths($template, $params)
{
$urls = [];
$alreadyPerform = [];
$paramsCounter = count($params);
for ($i = 0; $i < $paramsCounter; $i++) {
for ($j = 0; $j < $paramsCounter; $j++) {
if ($i !== $j && !in_array($params[$j], $alreadyPerform, true)) {
$urls[] = sprintf(
'/%s/%s/%s.html.twig', $params[$i], $params[$j], $template
);
}
}
$alreadyPerform[] = $params[$i];
$urls[] = sprintf('/%s/%s.html.twig', $params[$i], $template);
}
$urls[] = sprintf('%s.html.twig', $template);
return $urls;
}
This function work like I wanted until today (max 3 parameters), but I want to add one parameters today, maybe more after.
Thank you very much for your help !
Cheers.

Answer 1

Using recursion, you can do the following:
/**
* #param array $elements
* #param array $extra
*
* #return Generator
*/
function gen(array $elements, array $extra = []): \Generator {
foreach ($elements as $i => $head) {
foreach (gen(array_slice($elements, $i + 1), $extra) as $tail) {
yield array_merge([$head], $tail);
}
}
yield $extra;
}
demo: https://3v4l.org/gJB8q
Or without recursion:
/**
* #param array $elements
*
* #return Generator
*/
function gen2(array $elements): \Generator {
for ($num = count($elements), $i = pow(2, $num) - 1; $i >= 1; $i -= 2) {
$r = [];
for ($j = 0; $j < $num; $j += 1) {
if ($i & (1 << ($num - $j - 1))) {
$r[] = $elements[$j];
}
}
yield $r;
}
}
demo: https://3v4l.org/grKXo

Answer 2

Consider using the following package:
https://github.com/drupol/phpermutations
Just a very basic example of what it can do:
$permutations = new \drupol\phpermutations\Generators\Permutations(['A', 'B', 'C'], 2);
foreach ($permutations->generator() as $permutation) {
echo implode('/', $permutation);
echo "\n";
}
A/B
B/A
A/C
C/A
B/C
C/B