Problem 4 » 履歴 » リビジョン 2
リビジョン 1 (Noppi, 2023/12/27 01:36) → リビジョン 2/6 (Noppi, 2023/12/27 01:38)
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# [[Problem 4]]
```scheme
#!r6rs
#!chezscheme
(import (chezscheme))
(define (RotationNumber? num)
(let* ((num-string (number->string num))
(str-length (string-length num-string))
(count (div str-length 2)))
(let loop ((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 (answer-4)
(let loop1 ((num1 100)
(result 0))
(if (< 999 num1)
result
(let loop2 ((num2 100)
(result result))
(if (< 999 num2)
(loop1 (add1 num1) result)
(let ((num (* num1 num2)))
(if (RotationNumber? num)
(loop2 (add1 num2) (max result num))
(loop2 (add1 num2) result))))))))
(printf "4: ~D~%" answer-4)
```