public IGameState ApplyTurn(IGameState state)
    {
        TTTBoard board = (TTTBoard)state;

        board.SetPiece(x, player);
        if (board.player == TTTBoard.TTTPiece.X)
        {
            board.player = TTTBoard.TTTPiece.O;
        }
        else
        {
            board.player = TTTBoard.TTTPiece.X;
        }
        return(board);
    }