The map and pop suggestions work (very nice)... The $_ trick wont though, because (get this) $_ isn't actually empty at that point, it contains a single newline. Interestingly enough /^$/ will match a single newline.

perl -le '$_ = "\n"; print /^$/'
1
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So, a tested version of your code comes in at 69 chars....

#        1         2         3         4         5         6
#23456789012345678901234567890123456789012345678901234567890123456789
map{$n=$o=$_;for$c(@_){$n+=s/$c//}/^$/&&push@{$w[$n]},$o}<D>;@{pop@w}
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Update: The following code illustrates the issue a bit better...
Notice how /^$/ && is not identical to $_ || and in this example the difference is critical:

#!/usr/bin/perl -wT
use strict;

my @arr             = ("\n","dog\n","cat\n");
my $patternmatch    = 0;
my $underscorematch = 0;

/^$/ && $patternmatch++    for @arr;
$_   || $underscorematch++ for @arr;

print "Patternmatch    = $patternmatch\n";     # <==  prints 1
print "Underscorematch = $underscorematch\n";  # <==  prints 0
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-Blake