Sujet : Re: palindromic number
De : Nobody447095 (at) *nospam* here-nor-there.org (B. Pym)
Groupes : comp.lang.lisp comp.lang.schemeDate : 15. Sep 2024, 07:02:46
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <vc5ppi$20bdd$1@dont-email.me>
References : 1
User-Agent : XanaNews/1.18.1.6
B. Pym wrote:
"A palindromic number reads the same both ways. The largest
palindrome made from the product of two 2-digit numbers is 9009
= 91 x 99. Find the largest palindrome made from the product of
two 3-digit numbers."
Gauche Scheme
(use srfi-13) ;; string-reverse
(define (divisor? n m) (= 0 (mod m n)))
"We don't need no stinkin' loops!"
(define (prod-of-3-dig-nums? n)
(let1 sq (exact-integer-sqrt n)
(any (is divisor? n) (lrange sq 999))))
(define (good? n)
(let1 s (number->string n)
(and (equal? s (string-reverse s))
(prod-of-3-dig-nums? n))))
(find good? (lrange 998001 0 -1))
===>
906609
Given:
(define-syntax is
(syntax-rules ()
[(is x)
(lambda (y) (equal? y x))]
[(is compare x)
(lambda (y) (compare y x))]
[(is key compare x)
(lambda (y) (compare (key y) x))]))
Let's start with Project Euler Problem 1 : "If we list all the natural
numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9.
The sum of these multiples is 23. Find the sum of all the multiples of
3 or 5 below 1000."
Gauche Scheme
(use srfi-1) ;; lset-union
(fold + 0 (lset-union = (lrange 3 1000 3) (lrange 5 1000 5)))
===>
233168