flengyel-4clojure-solution131.clj

;; flengyel's solution to Sum Some Set Subsets
;; https://4clojure.com/problem/131

(fn [s & ss]
  (letfn [
    (subsets [s]
      (if (empty? s)
         #{#{}}
         (let [x (set (list (first s))) 
               dx (clojure.set/difference s x) 
               t (subsets dx)]
               (clojure.set/union t 
             (map (partial into x) t)))))
   (nonempty-subsets [s]
     (clojure.set/difference (subsets s) #{#{}}))
   (setsums [s]
     (let [nonempty (nonempty-subsets s) 
           n (count nonempty)]
       (set (map #(reduce + %1) nonempty))))]
   (not (empty? (apply clojure.set/intersection (map setsums (conj ss s)))))))