look for evaluation function in tictactoe 3d game

Question

I'm trying to apply minimax algorithm for the game tictactoe 3D in c++. I'm struggling to find a good evaluation function for it.

Does anybody know where has good resource to find the evaluation function?

Thank you.

Answer 1

Here's what I'd use:

Go over all rows (in all directions). For each row, if it has only one player's marks, award that player points based on how many marks there are. You can have a lookup table mapping number of marks to score, which can be adjusted to get the best results. The final result will be the difference between the two players' scores.

Example (pseudocode):

const int markScore[4+1] = {0, 1, 3, 5, 99999}; //assuming 4x4x4 board
//The above values are arbitrary - adjust to what you think makes sense.

score = 0;
for all rows in all directions:
    count Xs and Os
    if (xs>0 && os==0)
        score += markScore[xs];
    else if (os>0 && xs==0)
        score -= markScore[os];
return score;

This should work well, because any row with only one player's marks gives that player a chance to win.

Answer 2

Heuristics are unnecessary. There are only 3^27 states, you can enumerate them all and compute optimal play.

Answer 3

The evaluation function for this game needs only to test for a winning position. The evaluation function should count the empty fields in the board because the more empty fileds the board has, the higher the score should be. To reduce the number of lines, rows and diagonals the evaluation function has to check, you can mirror and rotate the board.