Data commit

Task/Monty-Hall-problem/Common-Lisp/monty-hall-problem-1.lisp

@@ -0,0 +1,15 @@
+(defun make-round ()
+  (let ((array (make-array 3
+                           :element-type 'bit
+                           :initial-element 0)))
+    (setf (bit array (random 3)) 1)
+    array))
+
+(defun show-goat (initial-choice array)
+  (loop for i = (random 3)
+        when (and (/= initial-choice i)
+                  (zerop (bit array i)))
+          return i))
+
+(defun won? (array i)
+  (= 1 (bit array i)))

Task/Monty-Hall-problem/Common-Lisp/monty-hall-problem-2.lisp

@@ -0,0 +1,18 @@
+CL-USER> (progn (loop repeat #1=(expt 10 6)
+                      for round = (make-round)
+                      for initial = (random 3)
+                      for goat = (show-goat initial round)
+                      for choice = (loop for i = (random 3)
+                                         when (and (/= i initial)
+                                                   (/= i goat))
+                                           return i)
+                      when (won? round (random 3))
+                        sum 1 into result-stay
+                      when (won? round choice)
+                        sum 1 into result-switch
+                      finally (progn (format t "Stay: ~S%~%" (float (/ result-stay
+                                                                       #1# 1/100)))
+                                     (format t "Switch: ~S%~%" (float (/ result-switch
+                                                                         #1# 1/100))))))
+Stay: 33.2716%
+Switch: 66.6593%

Task/Monty-Hall-problem/Common-Lisp/monty-hall-problem-3.lisp

@@ -0,0 +1,14 @@
+;Find out how often we win if we always switch
+(defun rand-elt (s)
+  (elt s (random (length s))))
+
+(defun monty ()
+  (let* ((doors '(0 1 2))
+	 (prize (random 3));possible values: 0, 1, 2
+	 (pick (random 3))
+	 (opened (rand-elt (remove pick (remove prize doors))));monty opens a door which is not your pick and not the prize
+	 (other (car (remove pick (remove opened doors)))))	 ;you decide to switch to the one other door that is not your pick and not opened
+    (= prize other))) ; did you switch to the prize?
+
+(defun monty-trials (n)
+  (count t (loop for x from 1 to n collect (monty))))