Find the greatest product of five consecutive digits in the 1000-digit number [euler,clojure]

problem-008.clj

;;; Solution to Euler problem 008
;;
;; Find the greatest product of five consecutive digits in the 1000-digit number.

(ns euler)

(def number 7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450)

(defn digits
  "return the digits of a number as a list"
  [number]
  (map #(- (int %) (int \0)) (seq (str number))))

;; (digits number)

(defn why-so-slow?
  "Pseudocode:

   - start at index 0
   - take 5 digits
   - find their product
   - compare with the running max
   - update if necessary
   - take the next 5 numbers"
  [numbers]
  ;; because of the (take 5 ...) here!!
  (loop [acc 0 five (take 5 numbers)]
    (if (>= (count numbers) 5)
      (recur (max acc (reduce * five)) (take 5 (rest numbers))) acc)))