*cider-scratch*.txt

;; image at: http://take.ms/VaXll

(def g {:a {:white :a :black :b}
        :b {:white :d :black :c}
        :c {:white :g :black :d}
        :d {:white :c :black :e}
        :e {:white :f :black :f}
        :f {:white :b :black :g}
        :g {:white :e :black :a}})

(defn follow-black [k]
  (get-in g [k :black]))

(defn follow-white [k]
  (get-in g [k :white]))

(defn build-instructions [n]
  (let [counts (->> n
                    str
                    (re-seq #"\d")
                    (mapv read-string))
        next-fn (cycle [follow-black follow-white])]
    (drop-last
     (mapcat (fn [c nf] (repeat c nf))
             (interleave counts (repeat 1))
             next-fn))))

(defn compute [instructions]
  ((apply comp (reverse instructions)) :a))

(defn divisible-by-7? [n]
  (= :a (-> n build-instructions compute)))

;;(map #(do [% (divisible-by-7? %)]) (range 30))
;;=> [[0 true]
[1 false]
[2 false]
[3 false]
[4 false]
[5 false]
[6 false]
[7 true]
[8 false]
[9 false]
[10 false]
[11 false]
[12 false]
[13 false]
[14 true]
[15 false]
[16 false]
[17 false]
[18 false]
[19 false]
[20 false]
[21 true]
[22 false]
[23 false]
[24 false]
[25 false]
[26 false]
[27 false]
[28 true]
[29 false]]