In Tue, Sep 16, 2014 at 11:08 PM, Daniel Prager
<daniel.a.pra...@gmail.com> wrote:
> Here's a version of "inside-out" Fisher-Yates that should fit the bill:
>
> (define (fy-shuffle lst)
> (define v (list->vector lst))
> (for/list ([n (in-range (length lst) 0 -1)])
> (let* ([i (sub1 n)]
> [j (random n)]
> [v_j (vector-ref v j)])
> (when (not (= i j))
> (vector-set! v j (vector-ref v i)))
> v_j)))
I was thinking more of a direct translation, which (I think) is easier
to see that it's correct:
(define (shuffle l)
(define a (make-vector (length l)))
(for ([x (in-list l)] [i (in-naturals)])
(define j (random (add1 i)))
(unless (= j i) (vector-set! a i (vector-ref a j)))
(vector-set! a j x))
(vector->list a))
But the issues from my last email are still there.
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://barzilay.org/ Maze is Life!
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