use strict;
use File::Find;

my %temp;
find( sub { s/mrg$/did/; 
            /did$/ and $temp{$_}++; }, '.' );
my @files = grep { $temp{$_} == 1 } keys %temp;

print "@files";

##</code><code>##


use strict;
use File::Find;

my %temp;
find( sub { m/^(.+)\.(mrg|did)/ 
            and 
            push(@{$temp{"$1.did"}}, $2) }, '.' );
my @files = grep { @{ $temp{$_} } == 1 
                   and 
                   $temp{$_}->[0] eq 'did'
                 } sort keys %temp;
print "@files";