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unix1/rle.lisp

Last active February 26, 2016 14:57
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  1. unix1 revised this gist Feb 26, 2016. No changes.
  2. unix1 created this gist Feb 26, 2016.
    27 changes: 27 additions & 0 deletions rle.lisp
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,27 @@
    (defun rle-encode (lst)
    (reverse (rle-lib-encode lst nil)))

    (defun rle-lib-encode (lst acc)
    (if (null lst)
    acc
    (let ((curr (car lst))
    (prev (car acc))
    (cnt (car (cdr acc))))
    (if (equal curr prev)
    (rle-lib-encode (cdr lst) (cons curr (cons (+ cnt 1) (cdr (cdr acc)))))
    (rle-lib-encode (cdr lst) (cons curr (cons 1 acc)))))))

    (defun rle-decode (lst)
    (reverse (rle-lib-decode lst nil)))

    (defun rle-lib-decode (lst acc)
    (if (null lst)
    acc
    (let ((cnt (car lst))
    (chr (car (cdr lst))))
    (rle-lib-decode (cdr (cdr lst)) (rle-lib-seq chr cnt acc)))))

    (defun rle-lib-seq (chr cnt acc)
    (if (eql cnt 0)
    acc
    (rle-lib-seq chr (- cnt 1) (cons chr acc))))