How about this? Sum the number of products over categories to get the total number of products. Divide that total by the number of columns to get the average height of a column. Shift categories off an array of unused ones and push them onto the current column if the new total would be closer to the average than the old. Keep a running average as a tiebreaker.

That may have corner cases which it doesn't optimize, but it should be good enough and run a whole lot faster than exhaustive search.

Update: Here is a corner case that doesn't optimize this way: @heights = qw/ 25 23 24 35 3 40/; $cols = 5; More attention to the running average could fix that, but I'm sure loopholes would remain.