Postorder

Score: 59.09 (pass)

#!perl -l
for$}(pop=~/./g){@~=map/$}/?($`,$',$&):$_,@~,pop}print@~

Score: 62.10 (pass)

#!perl -l
@a=pop;for$b(pop=~/./g){@a=map/$b/?($`,$',$&):$_,@a}print@a

Score: 82.08 (pass)

My head hurts!

#!perl
for$b(pop=~/./g){$_=pop;/$b/||print&&redo;push@ARGV,$&,$',$`}print reverse$/,@ARGV

Score: 167.09 (pass)

#!perl
sub c{my($i,$p,$r,$x)=(pop||return,pop);$r=substr$p,0,1;$x=index$i,$r;c(substr($p,1,$x),substr($i,0,$x));c(substr($p,1+$x),substr($i,$x+1));$o.=$r}c pop,pop;print"$o
"