If it's a 10x10 grid and the robot gets 200 moves, wouldn't an optimal solution be to traverse the grid in a zig-zag pattern (i.e. left-to-right across row 1, go down to row 2 and traverse it right-to-left, etc), picking up cans as it goes? It certainly has enough moves to do so since the grid only contains 100 squares. Don't get me wrong...I thought the article was interesting, but there seems to be a pretty trivial optimal solution...