Data commit

Task/Perfect-shuffle/Racket/perfect-shuffle.rkt

@@ -0,0 +1,27 @@
+#lang racket/base
+(require racket/list)
+
+(define (perfect-shuffle l)
+  (define-values (as bs) (split-at l (/ (length l) 2)))
+  (foldr (λ (a b d) (list* a b d)) null as bs))
+
+(define (perfect-shuffles-needed n)
+  (define-values (_ rv)
+    (for/fold ((d (perfect-shuffle (range n))) (i 1))
+              ((_ (in-naturals))
+               #:break (apply < d))
+      (values (perfect-shuffle d) (add1 i))))
+  rv)
+
+(module+ test
+  (require rackunit)
+  (check-equal? (perfect-shuffle '(1 2 3 4)) '(1 3 2 4))
+
+  (define (test-perfect-shuffles-needed n e)
+    (define psn (perfect-shuffles-needed n))
+    (printf "Deck size:\t~a\tShuffles needed:\t~a\t(~a)~%" n psn e)
+    (check-equal? psn e))
+
+  (for-each test-perfect-shuffles-needed
+            '(8 24 52 100 1020 1024 10000)
+            '(3 11  8  30 1018   10   300)))