compress.lisp

;; '(0 0 1 0 0) => ((2 0) 1 (2 0))
;; CL-USER> (compress  '(3 3 4 3 3 2 1 1 1 1 0))
;; ((2 3) 4 (2 3) 2 (4 1) 0)

(defun compress (l1)		       
  (cond ((null (cdr l1)) '())
	(t (accum (car l1) 1 (cdr l1)))))

(defun accum (val acc lst)
  (cond ((null lst) (cons (comp-list val acc) nil))
	((eq val (car lst)) (accum val (1+ acc) (cdr lst)))
	(t (cons (comp-list val acc) (accum (car lst) 1 (cdr lst))))))

(defun comp-list (val acc)
  (if (> acc 1) (list acc val) val))

(defun decompress (lst)
  (cond  ((null lst) nil)
	 ((atom (car lst)) (cons (car lst) (decompress (cdr lst))))
	 ((consp (car lst)) (append (deep-decompress (car lst)) (decompress (cdr lst))) 
	  )))

(defun deep-decompress (lst)
  (if (zerop (car lst)) nil 
      (cons (second lst) (deep-decompress (list (1- (car lst)) (second lst))))))