Negamax Ai for TicTacToe

Ivan-Mark Debono · 2013-07-08T17:58:10

Hi all, I'm doing a simple TicTacToe so that I can implement a Negamax algorithm which I can later use for other abstract games. However I'm encountering problems whereby the AI doesn't play the best move, and it loses constantly. My suspect is the static evaluation function. Here it is: public int getScore() { int score = 0; CellState state = CellState.Empty; if ((cells[0] == cells[1] || cells[1] == cells[2]) && (cells[1] != CellState.Empty)) state = cells[1]; if ((cells[6] == cells[7] || cells[7] == cells[8]) && (cells[7] != CellState.Empty)) state = cells[7]; if ((cells[0] == cells[3] || cells[3] == cells[6]) && (cells[3] != CellState.Empty)) state = cells[3]; if ((cells[2] == cells[5] || cells[5] == cells[8]) && (cells[5] != CellState.Empty)) state = cells[5]; if (((cells[3] == cells[4] || cells[4] == cells[5]) && (cells[4] != CellState.Empty)) || ((cells[1] == cells[4] || cells[4] == cells[7]) && (cells[4] != CellState.Empty)) || ((cells[0] == cells[4] || cells[4] == cells[8]) && (cells[4] != CellState.Empty)) || ((cells[2] == cells[4] || cells[4] == cells[6]) && (cells[4] != CellState.Empty))) { state = cells[4]; } if (state == currentPlayer) score = getMaxScoreValue(); else if (state == currentPlayer.getOpponent()) score = -getMaxScoreValue(); return score; } Cells is just an array of size 9 that represent the board positions. CellState is just an enum with values {Empty(0), Player(1), Opponent(2)}. getmaxScoreValue just returns the highest score (65536), Is this static function complete or am I missing other conditions? Thanks, C

Artificial Intelligence Programming

Started by cryobuzz75 March 04, 2013 02:35 PM

12 comments, last by alvaro 10 years, 9 months ago

cryobuzz75

105

Author

March 06, 2013 07:41 AM

Thanks for the insight. So basically I start the scoring by calling getWon() and return maxscore, -maxscore or 0 depending if the game is won, lost or drawn. If this is not the case, the evluation function will check of other combinations.

I will implement this in the connect4 I'm doing to make sure that negamax works fine before adding extensions to it.