flengyel-4clojure-solution82.clj

;; flengyel's solution to Word Chains
;; https://4clojure.com/problem/82

(fn  [wordset] (letfn [(patronize [s] (re-pattern (apply str (interpose ".{0,1}" (map str (vec s))))))
          (onediff? [s t n] (let [v (vec s)
         w (vec t)]
        (= 1 (reduce + (for [i (range n)] (if (= (v i) (w i)) 0 1))))))
(linked? [s t]
  (let [a (count s)
        b (count t)]
     (cond 
  (= a b) (onediff? s t a)
	(= (inc a) b) (= 1 (count (re-seq (patronize s) t)))
	(= (inc b) a) (= 1 (count (re-seq (patronize t) s)))
	:else false))) 
(compose [p q]
  (if (and (linked? (last p) (first q))
           (empty? (clojure.set/intersection (set p) (set q)))
	   (not= (first p) (last q))) 
	   (vec (concat p q))))
(str2path [s]
  (set (map (fn [i] [i]) (vec s))))
(compose-paths [S T]
  (->> (for [p (vec S) q (vec T)] (compose p q))
       (filter identity) (set)))]
     (let [pathset (str2path wordset)
	n       (count wordset)]
    (not (empty? (nth (iterate (partial compose-paths pathset) pathset) (dec n)))))))