my @ids = (1, 3, 4, 12, 41, 43, 44);
my $id = 4;

sub addID {
  for ( $i=0; $i<scalar(@_); $i++ ) {
    $idMap{$_[$i]} = $i;
  }
}

addID(@ids);

printf("ID: $id, NEXT: %d, PREV: %d\n", $ids[$idMap{$id}+1], $ids[$idMap{$id}-1]);