Y箱

回文数の問題

10秒考えて戦略決定。
数字を作ってから3けたで割りきれるか確認する。

6桁だけでいいだろうと思ったけど、5桁の処理も作った。

;;
;; Problem 4  : 2011/4/7
(* 999 999)     ;998001
(* 100 100)     ;10000

(use 'clojure.contrib.math)

(defn palindromic-5-digit-num []
  (for [one (range 9 1 -1) two (range 9 0 -1) three (range 9 0 -1)]
    (sort (+ (* 10000 one) (* 1000 two) (* 100 three) (* 10 two) one))))

(defn palindromic-6-digit-num []
  (for [one (range 9 0 -1) two (range 9 -1 -1) three (range 9 -1 -1)]
    (+ (* 100000 one) (* 10000 two) (* 1000 three) 
       (* 100 three) (* 10 two) one)))

(defn is-multiple-of-three-digits? [n]
  (loop [tester (range 100 1000)]
    (let [target (first tester)]
      (cond (empty? tester) false
        (and (zero? (rem n target))
             (>= (/ n target) 100 )
             (< (/ n target) 1000))  (list target (/ n target))
         true (recur (rest tester))))))

(loop [digit-list (palindromic-6-digit-num)]
  (let [ans (is-multiple-of-three-digits? (first digit-list))]
    (if (seq? ans)
      [(first digit-list) ans]
      (recur (rest digit-list)))))

(loop [digit-list (palindromic-5-digit-num)]
  (let [ans (is-multiple-of-three-digits? (first digit-list))]
    (if (seq? ans)
      [(first digit-list) ans]
      (recur (rest digit-list)))))
;;