# [racket] shortest paths, resource allocation/scheduling

I am not too sure if this is less than quadratic ??
(define points (list->vector '(a b c d e f)))
(define l (vector-length points))
(define (gen org start end)
(for/list ([n (in-range start end )])
(cons (vector-ref points org ) (vector-ref points n ))))
(for/fold ([accum empty]) ([i (in-range l)])
(append accum (gen i (+ i 1) l)))
On Mon, Dec 5, 2011 at 9:10 PM, Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
>* On Mon, Dec 5, 2011 at 10:00 AM, Geoffrey S. Knauth <geoff at knauth.org> wrote:
*>>* I'm wondering if there is something in the now very rich set of Racket libraries that already does this. Let's say I have 5 points {A,B,C,D,E}. I want to interconnect all of them:
*>>*
*>>* {AB,AC,AD,AE,AF,BC,BD,BE,BF,CD,CE,CF,DE,DF,EF}
*>>*
*>>* That's 15 edges rather than the 5x5=25 that a dumb interconnect would do. To start, I just need to track and sort the edge weights, and AB is the same as BA.
*>*
*>* Here's the start of an answer (sadly quadratic, but for N=121 I don't
*>* think that will matter much):
*>*
*>* #lang racket
*>* (require unstable/sequence)
*>* (define (subsets-of-size-2 l)
*>* (for*/lists (r) ([i l] [j l]
*>* #:unless (eq? i j)
*>* #:unless (member (cons j i) r))
*>* (cons i j)))
*>*
*>* (for ([(p q) (in-pairs (subsets-of-size-2 '(A B C D E F)))])
*>* (printf "~a <-> ~a\n" p q))
*>*
*>* --
*>* sam th
*>* samth at ccs.neu.edu
*>*
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