Trying to make unbeatable tic tac toe using minimax

Question

I am making a Tic-tac-toe and I am trying to make the computer always choose the optimal move. I did a lot of research in understanding minimax, but it doesn't seem to be working (AI is not making smart choises). I modified a code from a great article about this topic - check it here . Could anyone help me find out what is wrong with my code?

private Move minimax(JButton[][] boardCopy, String player){

    if (getResult(boardCopy) == 2) {
        return new Move(10);
    } else if (getResult(boardCopy) == 1){
        return new Move(-10);
    } else if (getResult(boardCopy) == 3) {
        return new Move(0);
    }

    ArrayList<Move> possibleMoves = getListOfPossibleMoves(boardCopy);

    for (Move move : possibleMoves){

        int i = move.i;
        int j = move.j;

        boardCopy[i][j].setText(player);

        if (player.equals(compPlayer)) {

            Move resMove = minimax(boardCopy, humanPlayer);
            move.moveScore = resMove.moveScore;

        } else {

            Move resMove = minimax(boardCopy, compPlayer);
            move.moveScore = resMove.moveScore;

        }

        boardCopy[i][j].setText("");
    }

    Move bestMove = new Move();
    if (player.equals(compPlayer)){

        int bestScore = -10000;
        for(Move move : possibleMoves){

            if (move.moveScore > bestScore){

                bestScore = move.moveScore;
                bestMove = new Move(move);
            }
        }
    } else {

        int bestScore = 10000;
        for(Move move : possibleMoves){

            if (move.moveScore < bestScore){

                bestScore = move.moveScore;
                bestMove = new Move(move);
            }
        }
    }

    return bestMove;
}

private void optimalComputerMove(JButton[][] board, String player){

    if (hasWinner) return;

    JButton[][] boardCopy = copyBoard(board);
    Move bestMove = minimax(boardCopy, player);
    int i = bestMove.i;
    int j = bestMove.j;
    board[i][j].setText(player);
    moveCount++;
    showResult(getResult(board));

}

private ArrayList<Move> getListOfPossibleMoves(JButton[][] board){

    ArrayList<Move> possibleMoves = new ArrayList<>();

    for (int i = 0; i < 3; i++){
        for(int j = 0; j < 3; j++){

            if (board[i][j].getText().equals("")){
                Move availMove = new Move(i, j);
                possibleMoves.add(availMove);
            }
        }
    }

    return possibleMoves;
}

EDIT:

GetResult method:

private int getResult(JButton[][] board){

    if((board[0][0].getText().equals(currPlayer) && board[1][0].getText().equals(currPlayer) && board[2][0].getText().equals(currPlayer)) ||
       (board[0][1].getText().equals(currPlayer) && board[1][1].getText().equals(currPlayer) && board[2][1].getText().equals(currPlayer)) ||
       (board[0][2].getText().equals(currPlayer) && board[1][2].getText().equals(currPlayer) && board[2][2].getText().equals(currPlayer)) ||
       (board[0][0].getText().equals(currPlayer) && board[0][1].getText().equals(currPlayer) && board[0][2].getText().equals(currPlayer)) ||
       (board[1][0].getText().equals(currPlayer) && board[1][1].getText().equals(currPlayer) && board[1][2].getText().equals(currPlayer)) ||
       (board[2][0].getText().equals(currPlayer) && board[2][1].getText().equals(currPlayer) && board[2][2].getText().equals(currPlayer)) ||
       (board[0][0].getText().equals(currPlayer) && board[1][1].getText().equals(currPlayer) && board[2][2].getText().equals(currPlayer)) ||
       (board[2][0].getText().equals(currPlayer) && board[1][1].getText().equals(currPlayer) && board[0][2].getText().equals(currPlayer))){

        if(board == this.board){
            hasWinner = true;
        }

        if (currPlayer.equals(humanPlayer)) return 1; //X won
        else return 2; //O won
    }

    boolean full = true;

    for(int i = 0; i < 3 && full; i++){
        for(int j = 0; j < 3 & full; j++){
            if (board[i][j].getText().equals("")){
                full = false;
            }
        }
    }

    if (full) {

        if (board == this.board){
            hasWinner = true;
        }

        return 3; //tie
    }
    else return 0; //incomplete

}

Which version of `tic-tac-toe` do you refer to? How many boards are there? — KaiserKatze, Aug 29 '18 at 11:32
You may take a look on [this](https://stackoverflow.com/questions/10679269/tic-tac-toe-with-minimax-computer-sometimes-losing-when-player-goes-first-work?rq=1) — samabcde, Aug 29 '18 at 11:36

score 0 · Answer 1 · answered Aug 29 '18 at 12:46

0

Your minimax doesn't count anything As you can see, it just returns from the function from the first ifs:

 if (getResult(boardCopy) == 2) {
        return new Move(10);
    } else if (getResult(boardCopy) == 1){
        return new Move(-10);
    } else if (getResult(boardCopy) == 3) {
        return new Move(0);
    }

answered Aug 29 '18 at 12:46

dehasi

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I was thinking of this as a base case in my recursion, and I am guessing this is the problem. However, not sure how to solve it... – Marijana Aug 29 '18 at 13:17

Trying to make unbeatable tic tac toe using minimax

1 Answers1