I was able to come up with

sub{my%r;for(split$",shift){$h=$p=$i=0;while(/./g){if($p){$h+=('/'eq$&
+)*2-1if$&eq$p}else{$h='/'eq$&}$p=$&;$r{$i++,$h}=1}}keys%r}
[download]

which is too long, but I don't have enough time to play with it any more :-(