I came up with this before reading fenLisesi's response, which uses the same "algorithm". Still, it's smaller, infinitesimally more efficient, and (very arguably) easier to follow.

Oh, and I generally come up with completely charred tomatoes mixed in between a combination of tough-as-boiled-beaver and still-dripping-blood beef chunks. (And don't forget the burned onions and the bloody carrot chunks resulting from my pathetic skewering skills, from which I end up with more holes in my thumb than in the vegetables.)

I shouldn't be allowed near a grill.

sub interleave {
    my ($a, $b) = @_;

    return scalar("B" x $b) if $a < 1;
    return "A" . ("B" x $b) if $a < 2;

    my $groups = $a - 1;
    my $bchunk = int($b / $groups);
    my $big = $b % $groups;

    return ("A" . ("B" x $bchunk)) x ($groups - $big)
         . ("A" . ("B" x ($bchunk + 1))) x $big
         . "A";
}
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