Time for an 2014 update…

Task/Average-loop-length/Ruby/average-loop-length.rb

@@ -0,0 +1,23 @@
+class Integer
+  def factorial
+    self == 0 ? 1 : (1..self).inject(:*)
+  end
+end
+
+def rand_until_rep(n)
+  rands = {}
+  loop do r = rand(1..n)
+    return rands.size if rands[r]
+    rands[r] = true
+  end
+end
+
+runs = 1_000_000
+
+puts " n\tavg\texp.\tdiff\n_____________________________"
+(1..20).each do |n|
+  sum_of_runs = runs.times.inject(0){|sum, _| sum += rand_until_rep(n)}
+  avg = sum_of_runs / runs.to_f
+  analytical = (1..n).inject(0){|sum, i| sum += (n.factorial / (n**i).to_f / (n-i).factorial)}
+  puts "%2d %8.4f %8.4f %8.4f" % [n, avg, analytical, (avg/analytical - 1)*100]
+end