player vs ai tic-tac-toe game using minimax algorithm in matlab

main.m
function playTicTacToe()

    % initialize game board
    board = zeros(3,3);
    
    % print empty board
    dispBoard(board);
    
    % game loop
    while true
        
        % player's turn
        [row, col] = getPlayerMove(board);
        board(row,col) = -1;
        dispBoard(board);
        
        % check if player wins
        if gameEnded(board)
            fprintf('Player wins!\n');
            return;
        end
        
        % AI's turn
        [row, col] = getAIMove(board);
        board(row,col) = 1;
        dispBoard(board);
        
        % check if AI wins
        if gameEnded(board)
            fprintf('AI wins!\n');
            return;
        end
        
        % check if board is full
        if all(board(:) ~= 0)
            fprintf('Game draw!\n');
            return;
        end
        
    end
        
end

function [row, col] = getPlayerMove(board)

    % prompt user for input until valid move is entered
    while true
        move = input('Your move (row,col): ');
        if board(move(1),move(2)) == 0
            row = move(1);
            col = move(2);
            return;
        else
            fprintf('Invalid move.\n');
        end
    end
    
end

function [row, col] = getAIMove(board)

    % use minimax algorithm to determine AI's move
    [val, idx] = max(minimax(board, 1));
    [row, col] = ind2sub(size(board), idx);
    
end

function [val, idx] = minimax(board, player)

    % base case: check if game ended
    if gameEnded(board)
        val = getScore(board, player);
        idx = nan;
        return;
    end
    
    % recursive case: apply minimax algorithm
    scores = nan(1,9);
    for i = 1:numel(board)
        if board(i) == 0
            boardNew = board;
            boardNew(i) = player;
            [scores(i), ~] = minimax(boardNew, -player);
        end
    end
    
    % player maximizes, AI minimizes
    if player == 1
        [val, idx] = max(scores);
    else
        [val, idx] = min(scores);
    end
    
end

function score = getScore(board, player)

    % calculate score based on which player wins or if draw
    if any(all(board(1:3,:) == player,1)) || any(all(board(:,1:3) == player,2)) || all(diag(board) == player) || all(diag(flipud(board)) == player)
        score = 1;
    elseif any(board(:) == 0)
        score = 0;
    else
        score = -1;
    end
    
end

function ended = gameEnded(board)

    % check if game ended based on whether someone won or board is full
    ended = any(all(board(1:3,:) == 1,1)) || any(all(board(:,1:3) == 1,2)) || all(diag(board) == 1) || all(diag(flipud(board)) == 1) || ...
            any(all(board(1:3,:) == -1,1)) || any(all(board(:,1:3) == -1,2)) || all(diag(board) == -1) || all(diag(flipud(board)) == -1) || ...
            all(board(:) ~= 0);

end

function dispBoard(board)

    % print current game board
    boardStr = {' ',' ',' ';' ',' ',' ';' ',' ',' '};
    boardStr(board == 1) = 'O';
    boardStr(board == -1) = 'X';
    fprintf('\n%s %s %s\n', boardStr{1,:});
    fprintf('%s %s %s\n', boardStr{2,:});
    fprintf('%s %s %s\n', boardStr{3,:});
    
end
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