Project Euler

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Problem 4 » 履歴 » リビジョン 3

リビジョン 2 (Noppi, 2023/12/27 01:38) → リビジョン 3/6 (Noppi, 2023/12/27 04:45)

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 # [[Problem 4]] 

 ```scheme 
 #!r6rs 
 #!chezscheme 

 (import (chezscheme)) 

 (define (RotationNumber? num) 
   (let* ([num-string ((num-string (number->string num)] num)) 
          [str-length (str-length (string-length num-string)] num-string)) 
          [count (count (div str-length 2)]) 2))) 
     (let loop ([index 0]) ((index 0)) 
       (cond 
         [(<= count index) #t] 
         [(equal? 
            (string-ref num-string index) 
            (string-ref num-string (- str-length 1 index))) 
          (loop (add1 index))] 
         [else #f])))) 

 (define answer-4 
   (let loop1 ([num1 100] [result 0]) ((num1 100) 
               (result 0)) 
     (if (< 999 num1) 
       result 
       (let loop2 ([num2 100] [result result]) ((num2 100) 
                   (result result)) 
         (if (< 999 num2) 
           (loop1 (add1 num1) result) 
           (let ([num ((num (* num1 num2)]) num2))) 
             (if (RotationNumber? num) 
               (loop2 (add1 num2) (max result num)) 
               (loop2 (add1 num2) result)))))))) 

 (printf "4: ~D~%" answer-4) 
 ```