PHP fully arranged recursive algorithm code

function rank($base, $temp=null)
{
$len = strlen($base);
if($len <= 1)
{
echo $temp. $base.'';
}
else
{
for($i=0; $i< $len; ++$i)
{
rank(substr($base, 0, $ i).substr($base, $i+1, $len-$i-1), $temp.$base[$i]);
}
}
}
rank('123');
?> ;

However, after testing the results many times, we found that there is a problem: if there are the same elements, the entire arrangement will be repeated. For example, there are only three possible arrangements for '122': '122', '212', and '221'; but the above methods are repeated. Make slight modifications, add a flag to identify duplicates, and the problem is solved.

function fsRank($base, $temp=null)
{
static $ret = array();
$len = strlen($base);
if($len < = 1)
{
//echo $temp.$base.'';
$ret[] = $temp.$base;
}
else
{
for($i=0; $i< $len; ++$i)
{
$had_flag = false;
for($j=0; $j<$i; ++$j)
{
if($base[$i] = = $base[$j])
{
$had_flag = true;
break;
}
}
if($had_flag)
{
continue;
}
fsRank(substr($base, 0, $i). substr($base, $i+1, $len-$i-1), $temp.$base[$i]);
}
}
return $ret;
}
print ''; </li>
<li>print_r(fsRank('122'));</li>
<li>print '';
?>

The recursive algorithm of full arrangement is introduced. Here is a non-recursive algorithm implementation code for full arrangement of PHP arrays. You can refer to it.