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Task/Unbias-a-random-generator/CoffeeScript/unbias-a-random-generator.coffeescript

@@ -0,0 +1,29 @@
+biased_rand_function = (n) ->
+  # return a function that returns 0/1  with
+  # 1 appearing only 1/Nth of the time
+  cap = 1/n
+  ->
+    if Math.random() < cap
+      1
+    else
+      0
+
+unbiased_function = (f) ->
+  ->
+    while true
+      [n1, n2] = [f(), f()]
+      return n1 if n1 + n2 == 1
+
+stats = (label, f) ->
+  cnt = 0
+  sample_size = 10000000
+  for i in [1...sample_size]
+    cnt += 1 if f() == 1
+  console.log "ratio of 1s: #{cnt / sample_size} [#{label}]"
+
+for n in [3..6]
+  console.log "\n---------- n = #{n}"
+  f_biased = biased_rand_function(n)
+  f_unbiased = unbiased_function f_biased
+  stats "biased", f_biased
+  stats "unbiased", f_unbiased