d-2.rb

d-2.rb

def d(a, b, &block)
  va = a.is_a?(Array) ? 1 : 0
  vb = b.is_a?(Array) ? 2 : 0
  v = va + vb
  case v
  when 0
    block.call(a, b)
  when 1
    a.map do |e|
      d(e, b, &block)
    end
  when 2
    b.map do |e|
      d(a, e, &block)
    end
  when 3
    al = a.length
    bl = b.length
    s = [al, bl].max
    (0...s).collect do |e|
      d(a[e % al], b[e % bl], &block)
    end
  end
end