# frozen_string_literal: true
 
class Slide
  attr_accessor :dirs
 
  def initialize(field, dirs)
    @field = field.split.map { |s| s.split('') }
    @dirs = optimise(dirs.gsub(/[LR]+(?<m>[LR])|[UD]+(?<m>[UD])/, '\k<m>'))
  end
 
  def to_s
    @field.map(&:join).join($/)
  end
 
  def incline_all
    @dirs.each_char do |c|
      case c
      when ?L, ?R then incline(c)
      else
        rotate(:+)
        incline({?U => ?L, ?D => ?R}[c])
        rotate(:-)
      end
    end
  end
 
  private
 
  def optimise(dirs)
    s = dirs.gsub(/(?<m>.).\k<m>(?=.)|(?<m>(?<n>.).)\k<n>\z/, '\k<m>')
    s == dirs ? s : optimise(s)
  end
 
  def incline(dir)
    @field = @field.map do |a|
      f = case dir
          when ?R then ->c{c == ?.}
          when ?L then ->c{c != ?.}
          end
      a.partition { |c| f[c] }.flatten
    end
  end
 
  def rotate(dir)
    ary = @field.transpose
    @field = case dir
             when :+ then ary.reverse
             when :- then ary.map(&:reverse)
             end
  end
end
 
samples = [[<<~EOT, 'UR'], [<<~EOT, 'LRRLLUDRRLRLRRURRRRLLLRULDUDULDLLRDULURULUDLDLUDDL']]
  ...
  .a.
  ...
EOT
  .....
  .d.i.
  kmegk
  ..tu.
EOT
 
samples.each do |field, dirs|
  s = Slide.new(field, dirs)
  s.incline_all
  puts "%s%s optimised => %s\n%s\n\n" % [field, dirs, s.dirs, s]
end
 

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