# 
# Here's my solution.  Nice and short.  I had also forgotten about sequences
# which appear twice in the same word.  $seq{$1} ne $_ was a quick fix for
# that bug.
# 
# Ronald
# 
# 
#!/usr/local/bin/perl -w

use strict;

my %seq;

open Q, ">questions" or die "Can't open 'questions': $!\n";
open A, ">answers" or die "Can't open 'answers': $!\n";

while (<>) {
  chomp;
  while (/(?=(.{4}))/g) {
    if (exists $seq{$1} and $seq{$1} ne $_) {
      $seq{$1} = 1;
    } else {
      $seq{$1} = $_;
    }
  }
}

for (sort (grep {$seq{$_} ne '1'} keys %seq)) {
  print Q "$_\n";
  print A "$seq{$_}\n";
}

__END__
