1_works.clj

;; this one correctly memoizes all the recursive calls

;(defn next-chain [n] a-new-number)

(def chain-ends nil)

(defn get-ans [n] (chain-ends n))
(def get-ans (memoize get-ans))

(defn chain-ends [n]
  (cond
    (= n 1)  1
    (= n 89) 89
    :else (get-ans (next-chain n))))

2_doesntwork.clj

;; this one doesn't. only the calls I make to chian-ends gets memoized
;; the internal recursive calls don't seem to get added to the memo.

(defn chain-ends [n]
  (cond
    (= n 1)  1
    (= n 89) 89
    :else (chain-ends n)))      


(def chain-ends (memoize chain-ends))

3_theotherstuff.clj

(defn split [n]
  (cond
    (< n 10) [n]
    :else (conj
            (split (quot n 10))
            (rem n 10))))


(defn next-chain [n]
  (reduce + (map #(* % %) (split n))))
                                          

my_full_solution.clj

(defn split [n]
  (cond
    (< n 10) [n]
    :else (conj
            (split (quot n 10))
            (rem n 10))))


(defn next-chain [n]
  (reduce + (map #(* % %) (split n))))


(def chain-ends nil)
(defn get-ans [n] (chain-ends n))
(def get-ans (memoize get-ans))

(defn chain-ends [n]
  (cond
    (= n 1)  1
    (= n 89) 89
    :else (get-ans (next-chain n))))



(prn (time
  (count
    (filter
      #(= % 89)
      (map chain-ends (range 1 10000000))))))


;; "Elapsed time: 20488.703 msecs"
;; 8581146