ariarule-4clojure-solution116.clj

;; ariarule's solution to Prime Sandwich
;; https://4clojure.com/problem/116

(fn [n]
   (letfn [(is-prime? [n]
             (if (= 2 n)
               true
               (if (or (= 1 n) (and (even? n) (> 2)))
                 false
                 (not (reduce #(or %1 (integer? (/ n %2))) false (range 3 n))))))]
    (if (is-prime? n)
     (let [primes-l (filter is-prime? (drop 1 (range)))
           prev-prime (last (take-while #(< % n) primes-l))
           next-prime (first (drop-while #(>= n %) primes-l))]
       (if prev-prime  
         (= n (/ (+ (last (take-while #(< % n) primes-l))
                    (first (drop-while #(>= n %) primes-l)))
                 2))
           false))
      false)))