||Well, I do actually quite like A and J. I heard the invalid input was on J, which is a bummer, because I think that was by far the best problem on the set.
My main complaints are (a) lack of variety, and (b) lack of problems requiring any kind of original insight. The lack of variety is obvious - FOUR geometry problems, and then B and G. If you replaced geometry with graph theory or DP or something, maybe that would be ok. But 4 problems where your biggest concerns have to do with questions like, "do these lines intersect"? Blech. The lack of insight is more subjective, but I think its perhaps even more obvious.
- The hardest problem should be the one requiring the most insight. Yet for H, all you want to do is understand overlapping triangles. I have seen an algorithm in at least two different courses that solves this problem directly. Its just a pain to implement.
- Problem E is basically shortest path on the plane with a polygon removed. This has been asked on an ACM before.
- Problem D is basically, "Do you know Pick's theorem?"
- Problems F and G? Hello, complete search.
I haven't really looked at problem I yet because I'm not a fan of physics in contests, but of the remaining problems (other than J), its hard to classify a single one of them as requiring serious original insight. For the ACM world finals, that is poor.