Posted 17 April 2013 - 04:02 AM
If you explore a position using minimax and you get a winning or losing score, you can store the simplified graph of the position (or some hash of it) and its score. Over time you can build a database of endgame positions that way, and then you can query this database in the search. If the graphs simplify as much as I think they will, this should allow you to deduce the true score of positions from pretty early on in the game.
I have one thought about this game that might be relevant: This game is played on a graph, in the sense that the geometry of the hexagonal pattern (e.g., what's aligned) does not matter. It could be played on any other graph just fine. Towards the end of the game, small groups that cannot grow because they are totally blocked by the other color are irrelevant and can be removed from the internal description of the board. Similarly, large groups are equivalent, whether they have 5 stones or 15. This allows to simplify the graph structure towards the end of the game. The are more simplifications available, like identifying "pass" cells (empty cells where you can prove that it won't matter whether they end up being black or white) and ignoring what they attach to. I believe only the parity of the number of "pass" cells on the board really matters.