p13.lisp

;;;; (**) Run-length encoding of a list (direct solution).

;;;; Implement the so-called run-length encoding data compression
;;;; method directly. I.e. don't explicitly create the sublists
;;;; containing the duplicates, as in problem P09, but only count
;;;; them. As in problem P11, simplify the result list by replacing
;;;; the singleton lists (1 X) by X.

;;;; Example:
;;;; * (encode-direct '(a a a a b c c a a d e e e e))
;;;; ((4 A) B (2 C) (2 A) D (4 E))

;;; I already implemented this method as
;;; encode-modified-loop. Renaming it here to encode-direct.
(in-package :99-problems)

(defvar encode-direct)
(setf (symbol-function 'encode-direct) #'encode-modified-loop)