From: Edward Faulkner <ef@...>
Date: 2006-01-23T18:47:49+09:00
Subject: Re: [QUIZ][SOLUTION] Grid Folding (#63)

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This is the kind of problem where it makes sense to trade off
efficiency for simplicity. =20


class Paper
  def initialize(width, height)
    @grid =3D Array.new(width) { Array.new(height) }
    height.times { |y| width.times {|x| @grid[x][y] =3D [width*y+x+1] }}
  end

  def width; @grid.size; end
  def height; @grid[0].size; end

  def answer
    raise "Not enough folds" if width > 1 or height > 1
    @grid[0][0]
  end

  # Fold right side over to left
  def fold!
    raise "Bad input" if width%2 =3D=3D 1
    @grid =3D (0 .. (width / 2 - 1)).map { |col|
      @grid[col].zip(@grid[width - col - 1]).map {|pair| pair[1].reverse + =
pair[0]}
    }
  end

  # 90 degree counter clockwise rotation
  def rotate!
    @grid =3D @grid.transpose.map{|c| c.reverse}
  end
end

def fold(width, height, commands)
  turns =3D commands.tr('RBLT', '0123').split(//).map{|x| x.to_i}
  paper =3D Paper.new(width, height)
  turns.each { |turn|
    4.times {|i|
      paper.fold! if i=3D=3Dturn
      paper.rotate!
    }
  }   =20
  paper.answer
end

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