Factorial using Hash

factorial.rb

factorial = Hash.new do |hash, key|
  if key > 1
    hash[key] = hash[key - 1] * key
  else
    hash[key] = 1
  end
end

factorial[1] # 1
factorial[2] # 2
factorial[3] # 6
factorial[4] # 24
factorial[5] # 120
factorial # { 1 => 1, 2 => 2, 3 => 6, 4 => 24, 5 => 120 }