ホーム - Project Euler

Problem 8¶

#!r6rs
#!chezscheme

(import (chezscheme))

(define Problem8-number-string
  (string-append "73167176531330624919225119674426574742355349194934"
                 "96983520312774506326239578318016984801869478851843"
                 "85861560789112949495459501737958331952853208805511"
                 "12540698747158523863050715693290963295227443043557"
                 "66896648950445244523161731856403098711121722383113"
                 "62229893423380308135336276614282806444486645238749"
                 "30358907296290491560440772390713810515859307960866"
                 "70172427121883998797908792274921901699720888093776"
                 "65727333001053367881220235421809751254540594752243"
                 "52584907711670556013604839586446706324415722155397"
                 "53697817977846174064955149290862569321978468622482"
                 "83972241375657056057490261407972968652414535100474"
                 "82166370484403199890008895243450658541227588666881"
                 "16427171479924442928230863465674813919123162824586"
                 "17866458359124566529476545682848912883142607690042"
                 "24219022671055626321111109370544217506941658960408"
                 "07198403850962455444362981230987879927244284909188"
                 "84580156166097919133875499200524063689912560717606"
                 "05886116467109405077541002256983155200055935729725"
                 "71636269561882670428252483600823257530420752963450"))

(define answer-8
  (let ((count (- (string-length p8-num-string) 13)))
    (let loop ((index 0) (max-num 0))
      (if (< count index)
        max-num
        (let* ((sub-num (substring Problem8-number-string index (+ index 13)))
               (char-lis (string->list sub-num))
               (num-lis (map
                          (lambda (char)
                            (- (char->integer char)
                               (char->integer #\0)))
                          char-lis))
               (product-num (fold-left * 1 num-lis)))
          (loop (add1 index) (max max-num product-num)))))))

(printf "8: ~D~%" answer-8)