Codeforces#290 Div2-A

290-div2-a.rb

# http://codeforces.com/contest/510/problem/A
class Snake
  def initialize(n, m)
    @n, @m = n, m
  end

  def draw
    rows.each { |row| puts row.join }
  end

  private

  def rows
    [].tap do |rows|
      @n.times do |idx|
        case
        when idx.even?
          rows << ['#'] * @m
        when rows[idx - 2].nil?, rows[idx - 2].first == '#'
          rows << ['.'] * (@m - 1) + ['#']
        else
          rows << ['#'] + ['.'] * (@m - 1)
        end
      end
    end
  end
end

n, m = gets.chomp.split.map(&:to_i)
snake = Snake.new(n, m)
snake.draw