I'm not sure that its more efficient, but you could try:

  # create pairs
  my @tmp = map { $_, $_ } @filenames;

  # rotate
  push @tmp, shift @tmp;

  # create the result
  my %next = @tmp;
  my %prev = reverse @tmp;
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In this code, the hashes form loops: to avoid that, replace the rotate step by code that remove the first and last elements. --Dave