pascalsTriangle

def pascalsTriangle(n)
  return [] if n < 0
  return [1] if n == 0

  ret = Array.new(n, []).map.each_with_index {|a, i| a = Array.new(i+1,1)}

  (1..n-1).each do |y|
    (0..y).each do |x|
      idy1 = y - 1
      idx1 = x - 1
      idy2 = y - 1
      idx2 = x
      s1 = idy1 >= 0 && idx1 >= 0 && !ret[idy1][idx1].nil? ? ret[idy1][idx1] : 0
      s2 = idy2 >= 0 && idx2 >= 0 && !ret[idy2][idx2].nil? ? ret[idy2][idx2] : 0
      ret[y][x] = s1+s2
    end
  end
  ret.flatten
end