sub compare{
  return 0 unless length $_[0] == length $_[1];
  return 1 if $_[0] eq $_[1];
  my $diff = 0;
  my @l1 = split //, $_[0];
  my @l2 = split //, $_[1];
  for(my $i = 0; $i < scalar @l1; $i++){
    $diff++ if $l1[$i] ne $l2[$i];
    return 0 if $diff > 1;
  }
  return 1;
}