You can make it work like this though:

++$count{$1},pos($genome)-- while $genome =~ /\G(..)/g
[download]

This however turns out to be a lot slower (seems to do a complete linear search for the proper string start every time):

$genome =~ /./g;
$count{$1}++ while $genome =~ /(.\G.)/g
[download]

update This however means that the lookahead version can be speeded up by about 5% too:

$count{$1}++ while $genome =~ /\G(?=(..))./g
[download]

You're only doing half the work now :-)

But if I understand gene work (not a certainty at all), I'm doing the half they actually want to do. :-P A molecule isn't paired with both of its neighbors, they are grouped two-by-two.

At least now I understand why they were doing the lookahead.

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