Data commit

Task/Knuth-shuffle/Scheme/knuth-shuffle-1.ss

@@ -0,0 +1,18 @@
+#!r6rs
+(import (rnrs base (6))
+        (srfi :27 random-bits))
+
+(define (semireverse li n)
+  (define (continue front back n)
+    (cond
+      ((null? back) front)
+      ((zero? n) (cons (car back) (append front (cdr back))))
+      (else (continue (cons (car back) front) (cdr back) (- n 1)))))
+  (continue '() li n))
+
+(define (shuffle li)
+  (if (null? li)
+      ()
+      (let
+          ((li-prime (semireverse li (random-integer (length li)))))
+        (cons (car li-prime) (shuffle (cdr li-prime))))))

Task/Knuth-shuffle/Scheme/knuth-shuffle-2.ss

@@ -0,0 +1,22 @@
+#!r6rs
+(import (rnrs base (6))
+        (srfi :27 random-bits))
+
+(define (vector-swap! vec i j)
+  (let
+      ((temp (vector-ref vec i)))
+    (vector-set! vec i (vector-ref vec j))
+    (vector-set! vec j temp)))
+
+(define (countdown n)
+  (if (zero? n)
+      ()
+      (cons n (countdown (- n 1)))))
+
+(define (vector-shuffle! vec)
+  (for-each
+   (lambda (i)
+     (let
+         ((j (random-integer i)))
+       (vector-swap! vec (- i 1) j)))
+   (countdown (vector-length vec))))