Pascal's triangle

pascal.rb

exit if (level = ARGV[0].to_i) <= 0

def combination n, r
  return 1 if r == 0
  n.downto(n-r+1).inject(:*) / r.downto(1).inject(:*)
end

max_length = combination(level-1, (level-1)/2).to_s.length
ary = [1]
0.upto(level-1).each do |i|
  i.downto(1).each do |j|
    ary[j] = 0 if ary[j].nil?
    ary[j] += ary[j-1]
  end
  print ' ' * max_length * (level - i - 1)
  puts ary.map{|n|  "%#{max_length}d" % n }.join(' ' * max_length)
end