문제.

해답 예시

cards = [*1..n]
cards.shuffle
p cards 

cards = [*1..n]
cards.sort_by!{rand}
p cards

cards = Set.new
loop do
  cards << rand(max)
  if cards.size >= n
    p cards
    break
  end
end

사용fisher-yates의 혼란 알고리즘
Fisher – Yates shuffle은 제한된 집합에서 무작위 배열을 생성하는 알고리즘입니다.이 방법은 유한열을 무작위의 다른 (흐트러진) 순서의 유한열로 다시 배열하는 것이다.

cards = [*1..n]
len = cards.length - 1
c = 0
len.step(1, -1) do |i|
  r = rand(i)
  c += 1
  cards[i], cards[r] = cards[r], cards[i]
end
p cards

cards = [*1..n]
shuffled = []
n.times do
  idx = rand(cards.length)
  shuffled << cards[idx]
  cards.delete_at(idx)
end
p cards

def factorial(number)
  number = 0 if number.nil?
  (1..number).inject(1,:*)
end

cards = [*1..n]
shuffled = []
r = rand(factorial(n))
(n-1).downto(1) do |i|
  quotient = r/factorial(i)
  excess = r%factorial(i)
  shuffled << cards.delete_at(quotient)
  r = excess
end
p shuffled