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From: DFS <nospam@dfs.com>
Newsgroups: comp.os.linux.advocacy
Subject: Re: Simple math/programming challenge for the "REAL programmer" Feeb
Date: Sun, 10 Mar 2024 14:55:28 -0400
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On 3/10/2024 11:59 AM, Yaxley Peaks wrote:
>> And got:
>> Error(s), warning(s):
>> *** - EVAL: undefined function SEQ-KEEP
> 
> SEQ-KEEP was added in emacs 29, what version are you using?
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Sequence-Functions.html#index-seq_002dkeep

As I said, I submitted it here:
https://rextester.com/l/common_lisp_online_compiler


Just post the output of your lisp code.

(defun kaprekarp (n)
   (let* ((num (* n n))
          (snum (number-to-string num))
          (num-digits (length (number-to-string n)))
          (num-list (string-split snum "" t))
          (right-side (reverse (take num-digits (reverse num-list))))
          (left-side (reverse (nthcdr num-digits (reverse num-list))))
          (left-side-num (string-to-number (mapconcat 'identity left-side)))
          (right-side-num (string-to-number (mapconcat 'identity 
right-side))))
     (= n (+ right-side-num left-side-num))))
(defun solve-problem (low high)
   (seq-keep (lambda (x)
               (and (kaprekarp x) x))
             (number-sequence low high)))
(solve-problem 1 100000000)