dict.pl

#!/usr/bin/perl 

$counter = 0;
$max_sub = "";
while (<>) {
    next if length $_ <= $counter + 1;
    chomp;
    my $tmp_str = substr $_, 0, $counter;
    for $letter (split //,(substr $_, $counter, -1)) {
        $tmp_str = $tmp_str . $letter;
        $suf{$tmp_str} = 0;
        if (exists $pref{$tmp_str} && ($counter < (length $tmp_str))) {
          $max_sub = $tmp_str;
          $counter = length $tmp_str;
        }
    }
    $_ = reverse $_;
    $tmp_str = reverse substr $_, 0, $counter;

    for $letter (split //, (substr $_, $counter, -1)) {
        $tmp_str = $letter . $tmp_str;
        $pref{$tmp_str} = 0;
        if (exists $suf{$tmp_str} && ($counter < (length $tmp_str))) {
            $max_sub = $tmp_str;
            $counter = length $tmp_str;
        }

    }
}

print "$max_sub\n";