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comp / comp.lang.python / Re: The "Strand" puzzle --- ( Continued Fractions using Lisp or Python? )

SubjectAuthor
* Re: The "Strand" puzzle --- ( Continued Fractions using Lisp or Python? )HenHanna
+- Re: The "Strand" puzzle --- ( Posting On Python-List Prohibited)Lawrence D'Oliveiro
`- Re: The "Strand" puzzle --- ( Continued Fractions using Lisp orPython? )B. Pym

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Subject: Re: The "Strand" puzzle --- ( Continued Fractions using Lisp or Python? )
From: HenHanna
Newsgroups: rec.puzzles, sci.lang, sci.math, comp.lang.lisp, comp.lang.python
Organization: A noiseless patient Spider
Date: Mon, 29 Jul 2024 18:58 UTC
References: 1 2
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From: HenHanna@devnull.tb (HenHanna)
Newsgroups: rec.puzzles,sci.lang,sci.math,comp.lang.lisp,comp.lang.python
Subject: Re: The "Strand" puzzle --- ( Continued Fractions using Lisp or
Python? )
Date: Mon, 29 Jul 2024 11:58:21 -0700
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On 7/26/2024 5:37 AM, IlanMayer wrote:
> On Thu, 25 Jul 2024 19:07:56 +0000, 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”
>>
>>
>>
>>   Ramanujan and Strand Puzzle
>>
>>             this was a very interesting puzzle tackled by the genius
>> Srinivasa Ramanujan.        In the year 1914, P.C. Mahalanobis, a Kings
>> college student in England, got hold of a puzzle from the Strand
>> magazine.
>
> Solution found at:
> https://ubpdqnmathematica.wordpress.com/2021/12/05/ramanujan-and-strand-puzzle/

thanks!

>>> So the solutions to the Strand puzzle can be found from the
continued fraction of \sqrt{2}, which _is_ satisfying simple.

>>> Using Mathematica to look at the first 10 convergents

---------- is this (also) easy to do using Lisp or Python???

Subject: Re: The "Strand" puzzle --- ( Posting On Python-List Prohibited)
From: Lawrence D'Oliv
Newsgroups: comp.lang.python
Organization: A noiseless patient Spider
Date: Mon, 29 Jul 2024 21:58 UTC
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From: ldo@nz.invalid (Lawrence D'Oliveiro)
Newsgroups: comp.lang.python
Subject: Re: The "Strand" puzzle --- ( Posting On Python-List Prohibited)
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On Mon, 29 Jul 2024 11:58:21 -0700, HenHanna wrote:

> ---------- is this (also) easy to do using Lisp or Python???

I threw this code together in about two minutes:

lo = 50
hi = 500
i = (lo + hi) // 2
while True :
losum = sum(range(lo, i))
hisum = sum(range(i + 1, hi + 1))
print(i, losum, hisum)
if losum == hisum :
break
if losum > hisum :
i = i - 1
else :
i = i + 1
#end if
#end while

and it seems there is no actual solution: it keeps oscillating between 355
and 356.

Subject: Re: The "Strand" puzzle --- ( Continued Fractions using Lisp orPython? )
From: B. Pym
Newsgroups: rec.puzzles, sci.lang, sci.math, comp.lang.lisp, comp.lang.python
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From: Nobody447095@here-nor-there.org (B. Pym)
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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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

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