Generate permutations PHP

[betazold]

<?php
 
function g($a, $u = [])
{
    $r = [];
    $size = sizeof($a);
    for ($i = 0; $i < $size; $i++) {
        if (empty($u[$i])) {
            $u[$i] = true;
            $vs = g($a, $u);
            $r[] = [$a[$i]];
            foreach($vs as $v) {
                $r[] = array_merge(array(
                    $a[$i]
                ) , $v);
            }
 
            $u[$i] = false;
        }
    }
 
    return $r;
}