Thanks Rodolfo and Eli for the education, very elegant solutions.
I really like the clever use of the "(and (right-triangle? a b c) (list a b
c))))" idiom.
I had to look up in-value... unfortunately the manual is a bit sparse
there, but I got the gift by running some examples... thanks.
After going "D'oh" about the infinite loop, here is the code I ended up
with:
(define (pythagorean-triple n)
(let loop-ab ([a 1] [b 2])
(define c (- n a b))
(cond [(>= a n) '()]
[(<= c b) (loop-ab (add1 a) (+ a 2))]
[(right-triangle? a b c) (list a b c)]
[else (loop-ab a (add1 b))])))
I noticed that the sequence-based solutions are quite a bit slower than the
code above probably because they don't short-cut on (<= c b), is there an
elegant way to speed them up?
Thanks again!
-joe
On Sun, Mar 18, 2012 at 11:25 PM, Eli Barzilay <e...@barzilay.org> wrote:
> 20 minutes ago, Rodolfo Carvalho wrote:
> >
> > (define (pythagorean-triple/alt n)
> > (for*/first ([a (in-range 1 n)]
> > [b (in-range a n)]
> > [c (in-value (- n a b))]
> > #:when (right-triangle? a b c))
> > (list a b c)))
>
> You can also use `for*/or':
>
> (define (pythagorean-triple/alt n)
> (for*/or ([a (in-range 1 n)]
> [b (in-range a n)])
> (define c (- n a b))
> (and (right-triangle? a b c) (list a b c))))
>
> --
> ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
> http://barzilay.org/ Maze is Life!
>
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