Problem description, from Project Euler

Find the greatest product of five consecutive digits in the 1000-digit number.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Solution

I decided to store the data in a text file. Not only would it save me from embedding the number in the source, but also give me an opportunity to try some simple file handling in Clojure. There is nothing super notable here, it’s another brute-force attempt.

; use to reduce a list into a string
(defn str-join [delim l]
    (reduce (fn [res cur] (str res delim cur)) l)
    )
; use to parse an integer out of a string
(defn parseInt [n]
    (Integer/parseInt n)
    )

(defn problem08 [filename digit-count]
    ; used to read the file and remove any newlines
    (defn get-normalized-file-contents [filename]
        (str-join "" (remove #(= % \newline) (slurp filename)))
        )

; used to obtain the maximum product
(defn find-numbers [haystack max-number]
    ; compute the product of the first 5 numbers in haystack
    (def tmp (reduce * 
        (map parseInt (map str (take digit-count haystack)))
        ))

    ; are there more digits to try? if so, recurse
    (if (>= (count haystack) digit-count)
        ; work with the rest of the list
        (find-numbers 
            (rest haystack) 
            ; pass to this function the greater of the current
            ; maximum and the product of the first 5 digits in
            ; the current list
            (if (> tmp max-number) tmp max-number)
            )
        ; otherwise, return what we have determines to be the max number
        max-number
        )
    )

(find-numbers
    (get-normalized-file-contents filename)
    -99
    )
)


(problem08 "/pathtofile/data.txt" 5)