project euler 80

pe_80.clj

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Problem 80  : 2012/4/26
;;"Elapsed time: 324.264961 msecs"


(require '[clojure.math.numeric-tower :as math])

(defn square-num? [n]
  (= (math/expt (int (Math/sqrt n)) 2) n))

(defn num-cat [[u l]]
  (+ (* u 10) l))

(defn biggest-x [bring-down tgt]
  (last (take-while #(< (second %) tgt)
                    (map #(vector % (* % (num-cat [bring-down %])))
                         (range 0 10)))))

(defn extract-sqrt [num & {:keys [p] :or {p 100}}]
  (loop [root [],
         tgt-digit num,
         bring-down-s 0N]
    (let [[x n-mul] (biggest-x bring-down-s tgt-digit)
          new-root (conj root x)]
      (if (>= (count new-root) p)
        new-root
        (recur new-root
               (* (- tgt-digit n-mul) 100)
               (+ (num-cat [bring-down-s x]) x))))))

(defn pe80 [limit]
  (reduce +
          (map #(reduce + (extract-sqrt %))
               (filter (complement square-num?)
                       (range 2 (inc limit))))))