sub checker
{
   my ($str) = @_;
   for ('00' .. '99')
   {
      my $n = 0;
      $n++ while $str =~ /$_/g;
      die "'$_' appears $n times\n" if $n != 1;
   }
}
 
sub generate
{
 0         1         2         3         4         5         6         7         8     
#01234567890123456789012345678901234567890123456789012345678901234567890123456789012345
 for$x(0..9){for$y(0..9){/$x$y/||(/^$y/and$_="$x$_")||(/$x$/and$_.=$y)or$_.="$x$y"}}$_ 
}
 
print "Generating ...\n";
my $test = generate();
print "$test\n";
 
print "Checking   ...\n";
checker($test);
 
print "Ok\n";
----
Generating ...
99001020304050607080911213141516171819223242526272829334353637383944546474849556575859667686977879889
Checking   ...
Ok