Submission #3215873

---

Source Code Expand

fac = [1]
(1..100).each{|i| fac[i] = fac[i-1]*i}
n = gets.to_i
c = n.times.map{gets.to_i}
e = [0] * n
(0...n).each do |i|
  (0...n).each do |j|
    e[j] += 1 if c[j]%c[i] == 0
  end
end
ans = 0
(0...n).each do |i|
  (0...n).each do |j|
    (0..n/2).each do |_k|
      k = _k * 2
      break if k > i || k > e[j]-1
      ans += fac[e[j]-1] / fac[k] / fac[e[j]-1-k]  *  fac[n-e[j]] / fac[i-k] / fac[n-e[j]+k-i]  *  fac[i] * fac[n-i-1] if 0 <= n-e[j]+k-i
    end
  end
end
ans = ans.to_r/fac[n]
printf("%.12f\n", ans.to_f)

Submission Info

Judge Result