Hi, I created the following code from some scheme I found on
ProjectEuler.net (problem #9):
(define (right-triangle? a b c)
(= (+ (* a a) (* b b)) (* c c)))
(define (pythagorean-triple n)
(let loop-a ([a 1])
(let loop-b ([b (add1 a)])
(let ([c (- n a b)])
(if (<= c b)
(loop-a (add1 a))
(if (right-triangle? a b c)
(list a b c)
(loop-b (add1 b)))))))
Is the following a better way to write this?
(define (pythagorean-triple n)
(let loop-ab ([a 1] [b 2])
(let ([c (- n a b)])
(if (<= c b)
(loop-ab (add1 a) (+ a 2))
(if (right-triangle? a b c)
(list a b c)
(loop-ab a (add1 b)))))))
I wish I could do "(let* loop-ab ([a 1] [b (add1 a)])...", but that is not
allowed. In any event, this second version of pythagorean-triple feels a
little better than the original to me. Of course taking the next step,
feels like going too far as it makes the relationship between n, c, a & b
harder to see:
(define (pythagorean-triple n)
(let loop-abc ([a 1] [b 2] [c (- n 3)])
(if (<= c b)
(loop-abc (add1 a) (+ a 2) (- n (+ 3 (* a 2))))
(if (right-triangle? a b c)
(list a b c)
(loop-abc a (add1 b) (- n (+ a (add1 b))))))))
Thoughts?
-joe
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