Postorder

Score: 51.10 (pass)

Trial and error pays off unexpectedly

#!perl -l
@ARGV[$_=pop]=~s^.^s~($&)(.*)~
$2
$1~^ge|print//

Score: 52.10 (pass)

Ahh, the empty regex. We'll miss you...

#!perl -l
$ARGV[$_=pop]=~s^.^s~($&)(.*)~
$2
$1~^ge|print//g

Score: 54.10 (pass)

Multiline s///

#!perl -l
$ARGV[$_=pop]=~s^.^s~($&)(.*)~
$2
$1~^ge|print/\w/g

Score: 55.09 (pass)

#!perl -l
$ARGV[$_=pop]=~s^.^s~($&)(\w*)~ $2 $1~^ge|print/\w/g

Score: 57.09 (pass)

Fun tiebreaker algorithm, Ton.

#!perl -l
$_=pop;($z=pop)=~s^.^s|($&)(\w*)| $2 $1|^ge;print/\w/g

Score: 59.13 (pass)

#!perl -l
$_=pop;($z=pop)=~s#.#s/($&)(.*?)\b/ $2 $1/#ge;print/\w/g

Score: 63.12 (pass)

#!perl -l
$_=pop;($z=pop)=~s#.#$z=$&,s/$z(.*?)\b/ $1 $z/#ge;print/\w/g

Score: 65.07 (pass)

#!perl -l
sub z{my$z=shift;map(&z,/[^$z]+/g),$z}$_=pop;print z pop=~/./g

Score: 67.07 (pass)

#!perl -l
sub z{my$y;map($_&&&z,split$y=shift),$y}$_=pop;print z pop=~/./g

Score: 72.07 (pass)

#!perl
sub r{map/$_[0]/&&&r,split my$n=shift;print$n}$_=pop;r pop=~/./g;print$/

Score: 79.07 (pass)

#!perl
sub r{/$p[$x]/&&r()for split my$n=$p[$x++];print$n}$_=pop;r@p=pop=~/./g;print$/