project euler 60

pe_60.clj

(use 'clojure.contrib.math)

(defn concat-num [n m]
  (let [zeros (first (drop-while #(<= % m) (iterate #(* 10 %) 1)))]
    (+ (* n zeros) m)))

(defn prime-pair? [n m]
  (and (is-prime? (concat-num n m))
       (is-prime? (concat-num m n))))

(defn all-make-prime-pair? [p-set p]
  (every? true? (map #(prime-pair? p %) p-set)))

(defn insert-pset [primeset-list pset]
  (loop [h-list []
	t-list primeset-list]
    (cond (empty? t-list) (conj h-list pset)
	  (> (count pset)(count (first t-list))) (concat h-list [pset] t-list)
	  :else (recur (conj h-list (first t-list))
		       (next t-list)))))

(defn create-next [primeset-list pnum]
  (filter #(all-make-prime-pair? (butlast %) (last %))
	  (map #(conj % pnum)
	       (conj primeset-list []))))

(defn pe60 [seq-count]
  (loop [primeset-list []
	 primes (cons 3 (drop 3 (get-prime-list)))] ;; remove 2 and 5
    (if (>= (count (first primeset-list)) seq-count)
      (first primeset-list)
      (let [nextset (create-next primeset-list (first primes))]
	(recur (reduce insert-pset primeset-list nextset)
	       (next primes))))))

;; "Elapsed time: 965709.946376 msecs"
;; ouch!