s99.clj

(ns s99)

(defn last-99 "P01" [l]
  (reduce #(do %2) l))

(last-99 '(1 3 5 6))

(defn penultimate "P02" [l]
  (first (rest (reverse l))))

(penultimate '(1 3 5 6))

(defn nth-s99 "P03" [n l]
  (if (= 0 n) (first l) (nth-s99 (- n 1) (rest l))))

(nth-s99 3 '(1 3 5 6 8 11))

(defn length "P04" [l]
  (if (empty? l) 0 (+ 1 (length (rest l)))))

(length '(1 3 5 6))

(defn reverse-s99 "P05" [l]
  (if (empty? l) nil (cons (last l) (reverse-s99 (butlast l)))))

(reverse-s99 '(1 3 5 6))

(defn palyndrome? "P06" [l]
  (= l (reverse l)))

(palyndrome? '(1 3 5 6))
(palyndrome? '(1 3 5 3 1))
(palyndrome? '(1 3 5 5 3 1))

(defn flatten "P07" [l]
  (reduce #(concat %1 (if (list? %2) (flatten %2) (list %2))) '() l))

(flatten '(1 3 (5 6) (8) (9 (11 12))))

(defn compress "P08" [l]
  (reduce #(if (= (last %1) %2) %1 (concat %1 (list %2))) '() l))

(compress '(1 1 3 1 3 3 5 6 6 7))

(defn pack "P09" [l]
  (reverse (reduce
   #(if (= (first (first %1)) %2)
      (cons (cons %2 (first %1)) (rest %1))
      (cons (list %2) %1 ))
   '()
   l))
  )

(pack '(1 1 3 1 3 3 5 6 6 7))

(defn encode "P10" [l]
  (map #(list (first %) (count %)) (pack l)))

(encode '(1 1 3 1 3 3 3 3 5 6 6 6 7))