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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: rec.puzzles,sci.lang,sci.math,comp.lang.lisp,comp.lang.python
Subject: Re: The "Strand" puzzle --- ( Continued Fractions using Lisp orPython? )
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Date: Thu, 1 Aug 2024 09:33:53 -0000 (UTC)
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HenHanna wrote:

> > > e.g. -------- For the (street)  Numbers (1,2,3,4,5,6,7,8)
> > > 
> > >        (1,2,3,4,5)  and  (7,8)  both add up to 15.
> > > 
> > > 
> > > 
> > > "In a given street of houses with consecutive numbers between
> > > 50 and 500, find the house number, for which, the sum of
> > > numbers on the left is equal to the sum of numbers on the
> > > right"

Gauche Scheme

(define (strand lst)
  (let go ((left-sum 0) (tail lst))
    (if (null? tail)
      #f
      (let ((right-sum (fold + 0 (cdr tail))))
        (cond ((< left-sum right-sum)
               (go (+ left-sum (car tail)) (cdr tail)))
              ((= left-sum right-sum) (car tail))
              (#t #f))))))

(strand '(1 2 3 4 5 6 7 8))
  ===>
6

(lrange 2 5)
  ===>
(2 3 4)

(any
  (lambda (n)
    (if (strand (lrange 50 n))
      n
      #f))
  (lrange 500 50 -1))
  ===>
352

(strand (lrange 50 352))
  ===>
251