Hi Tom,<div><br></div><div>thanks for the comments.</div><div><br></div><div>As far as reading the data into a vector, that can be accomplished with "(define vec (read in))" I was more interested in how to create an srfi/25 array from that vector.</div> <div><br></div><div>Thanks also for the example of using for*/fold.</div><div><br></div><div>-Joe</div><div><br></div><div><br><br><div class="gmail_quote">On Sat, Mar 24, 2012 at 11:26 PM, Tom McNulty <span dir="ltr"><<a href="mailto:tom.mcnulty@gmail.com">tom.mcnulty@gmail.com</a>></span> wrote:<br> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The format of prob11's data is already quite close to what the reader expects for a vector, so you can read it directly by including #( ...<br> <br> (define tbl<br> #(08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08<br> <snip> ...<br> 01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48))<br> <br> A convenience function to read the table is then:<br> <br> (define (get i j)<br> (vector-ref tbl (+ (* i 20) j)))<br> <br> Here is my across function, I use a for/fold loop. The vertical and diagonal cases are similar.<br> <br> (define (across)<br> (for*/fold ([mx 0])<br> ([i (in-range 0 20)]<br> [j (in-range 0 17)])<br> (max mx (* (get i j)<br> (get i (+ j 1))<br> (get i (+ j 2))<br> (get i (+ j 3))))))<br> <br> Does that help?<br> <br> <br> - Tom<br> <div><div class="h5"><br> On 2012-03-24, at 11:01 PM, Joe Gilray wrote:<br> <br> > I was playing around with ProjectEuler #11 and found a lisp solution and adapted it to Racket. Part of the solution had code like the following to find products of values in a 20x20 vector.<br> ><br> > (define (prod-of-vec-lines-of-length-4 v ix iy dx dy)<br> > (do ([p 1 (* p (if (in-vector? x y 20 20) (vector-ref v (+ (* 20 y) x)) 0))]<br> > [x ix (+ x dx)]<br> > [y iy (+ y dy)]<br> > [c 0 (add1 c)])<br> > ((= c 4) p)))<br> ><br> > I realize I've hard-coded this in a very ugly fashion to 20x20 vectors.<br> ><br> > My questions are:<br> ><br> > 1) Is there a more Racket-idiomatic way to write the "do" loop above?<br> > 2) If I wanted to use srfi/25 to do this in a nicer fashion, how would I read in the array? - I liked being able to read in the vector with simply (read in) - is there a simply , one-line way to convert a vector to an array (make-array (shape 0 20 0 20) vec) puts the entire 400 element vector into the first element of the array!<br> ><br> > Thanks,<br> > -joe<br> </div></div>> ____________________<br> > Racket Users list:<br> > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a><br> <br> </blockquote></div><br></div>