Data update

Task/Average-loop-length/Crystal/average-loop-length.cr

@@ -0,0 +1,26 @@
+struct Int
+  def factorial
+    raise "only positive" if self < 0
+    (1_i64..self.to_i64).product
+  end
+end
+
+def rand_until_rep (n)
+  rands = {} of Int32 => Bool
+  loop do
+    r = rand(1..n)
+    return rands.size if rands[r]?
+    rands[r] = true
+  end
+end
+
+runs = 1_000_000
+
+puts " N    average    exp.        diff   ",
+     "===  ========  ========  ==========="
+(1..20).each do |n|
+  sum_of_runs = runs.times.sum(0_i64) { rand_until_rep(n) }
+  avg = sum_of_runs / runs
+  analytical = (1..n).sum(0.0) {|i| (n.factorial / (n.to_f**i) / (n-i).factorial) }
+  puts "%3d  %8.4f  %8.4f  (%8.4f%%)" % {n, avg, analytical, (avg/analytical - 1)*100}
+end