Matt, Why use preg_split()? PHP strings *are* arrays of characters! Being something of a minimalist: function interleaveStrings($a, $b) { $max = max($al = strlen($a), $bl = strlen($b)); for ($i = 0; $i < $max; $i++) { if ($i < $al) $r .= $a[$i]; if ($i < $bl) $r .= $b[$i]; } return $r; } Probably more efficient would be to interleave the shorter length, and then concatenate the remainder of the longer. --doug > From: Matt Warden <mwarden at gmail.com> > Subject: Re: [thelist] PHP Challenge > To: "thelist at lists.evolt.org" <thelist at lists.evolt.org> > Interesting problem. > > Run: > http://mwarden.f2o.org/sandbox/interleaveStrings.php > > Source: > http://mwarden.f2o.org/sandbox/viewsource.php?linemode=0&f=interleaveStrings.php [snip] -- Douglas Clifton dwclifton at gmail.com http://loadaveragezero.com/ http://loadaveragezero.com/app/s9y/ http://loadaveragezero.com/drx/rss/recent