DouKaku?

def bingo(num)
  raise ArgumentError.new("fixnum only") unless num.kind_of? Fixnum
  raise ArgumentError.new("1 ijyou de onegai simasu") unless num >= 1

  results = []

  ary=(1..num).to_a
  ary.size.times{
    index = (rand * ary.size).to_i
    results << ary.delete_at(index)
  }

  results
end