new files

Task/Best-shuffle/Racket/best-shuffle.rkt

@@ -0,0 +1,20 @@
+#lang racket
+
+(define (best-shuffle s)
+  (define len (string-length s))
+  (define @ string-ref)
+  (define r (list->string (shuffle (string->list s))))
+  (for* ([i (in-range len)] [j (in-range len)])
+    (when (not (or (= i j) (eq? (@ s i) (@ r j)) (eq? (@ s j) (@ r i))))
+      (define t (@ r i))
+      (string-set! r i (@ r j))
+      (string-set! r j t)))
+  r)
+
+(define (count-same s1 s2)
+  (for/sum ([c1 (in-string s1)] [c2 (in-string s2)])
+    (if (eq? c1 c2) 1 0)))
+
+(for ([s (in-list '("tree" "abracadabra" "seesaw" "elk" "grrrrrr" "up" "a"))])
+  (define sh (best-shuffle s))
+  (printf " ~a, ~a, (~a)\n" s sh (count-same s sh)))