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Task/Move-to-front-algorithm/Common-Lisp/move-to-front-algorithm.lisp

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+(defconstant +lower+ (coerce "abcdefghijklmnopqrstuvwxyz" 'list))
+
+(defun move-to-front (x xs)
+  (cons x (remove x xs)))
+
+(defun enc (text table)
+  (map 'list
+       (lambda (c)
+               (let ((idx (position c table)))
+                 (setf table (move-to-front c table))
+                 idx))
+       text))
+
+(defun dec (indices table)
+    (coerce (mapcar (lambda (idx)
+                      (let ((c (nth idx table)))
+                        (setf table (move-to-front c table))
+                        c))
+                    indices)
+            'string))
+
+(loop for word in '("broood" "bananaaa" "hiphophiphop")
+      do (let* ((encoded (enc word +lower+))
+                (decoded (dec encoded +lower+)))
+           (assert (string= word decoded))
+           (format T "~s encodes to ~a which decodes back to ~s.~%"
+                   word encoded decoded)))