Great article on this problem: http://www.americanscientist.org/issues/pub/2002/3/the-easiest-hard-problem

The article also lists a notoriously hard example: assert checkio([771, 121, 281, 854, 885, 734, 486, 1003, 83, 62]) == 0

But continuous to note that most greedy algorithms only get 32 or 26 as the best result. I recommend that this example is added to the hidden tests.