use strict;
use warnings;

# @data contains the (chomped, lower-cased) entries
# from a 70K dictionary file (2076 words beginning with 'j')

my $count;        # Or whatever: this can check algorithm validity
foreach my $item ( @data ) {
   compare( $item, $_  ) and $count++ for @data;
}
print $count;

sub compare {
   return 0 unless length $_[0] == length $_[1];
   my $diff = 0;
   for ( 0 .. length $_[0] ) {
      $diff++ if substr( $_[0], $_, 1 ) ne substr( $_[1], $_, 1 );
      return 0 if $diff > 1;
   }
   return 1;
}