Here is my version. Took me less than 5 minutes and worked the first time:

  def pascal(num)
    return [1] if num == 1
    res = []
    prev = [0] + pascal(num-1) + [0]
    (1..num).to_a.each { |i| res << (prev[i-1] + prev[i]) }
    return res
  end