99 Problems in Lisp (Part IV)

P11 - Modified Run length encoding

(defn encode-modified [lst]
  ((fn [xs accum]
     (if (= nil xs)
       accum
       (recur (rest xs) 
       (concat accum 
        (list 
         (if (= (count (first xs)) 1)
    (ffirst xs)
    (list (count (first xs)) (ffirst xs)))))))) (pack-list lst) nil))

P12 - Decode a run length encoding list

(defn decode [lst]
  ((fn [xs accum]
     (if (= nil xs)
       accum
       (recur (rest xs)
       (if (list? (first xs))
  (concat accum (replicate (ffirst xs) (first (rfirst xs))))
  (concat accum (list (first xs))))))) lst nil))