Postorder

Score: 57.17 (pass)

#!perl
$_="@ARGV";s/$+/ /g,$/=$&.$/while/(\S).*\1\S* *$/;print$/

Score: 58.19 (pass)

#!perl
$_="@ARGV";/[$+]/,s/$&/ /g,$/=$&.$/while/.* (\S+)/;print$/

Score: 60.30 (pass)

#!perl
$_="@ARGV";/[$+]/,$/=$&.$/,s/$&/ /g while/ (\S+) *$/;print$/

Score: 64.17 (pass)

#!perl
($y,$_)=@ARGV;$y=~/[$+]/,$/=$&.$/,s/$&/ /while/(\S+) *$/;print$/

Score: 67.14 (pass)

#!perl -l
($y,$_)=@ARGV;$y=~/[$+]/,$z=$&.$z,s/$&/ /while/(\S+) *$/;print$z