Hi Tom, thanks for the comments.
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. Thanks also for the example of using for*/fold. -Joe On Sat, Mar 24, 2012 at 11:26 PM, Tom McNulty <tom.mcnu...@gmail.com> wrote: > 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 #( ... > > (define tbl > #(08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08 > <snip> ... > 01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48)) > > A convenience function to read the table is then: > > (define (get i j) > (vector-ref tbl (+ (* i 20) j))) > > Here is my across function, I use a for/fold loop. The vertical and > diagonal cases are similar. > > (define (across) > (for*/fold ([mx 0]) > ([i (in-range 0 20)] > [j (in-range 0 17)]) > (max mx (* (get i j) > (get i (+ j 1)) > (get i (+ j 2)) > (get i (+ j 3)))))) > > Does that help? > > > - Tom > > On 2012-03-24, at 11:01 PM, Joe Gilray wrote: > > > 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. > > > > (define (prod-of-vec-lines-of-length-4 v ix iy dx dy) > > (do ([p 1 (* p (if (in-vector? x y 20 20) (vector-ref v (+ (* 20 y) > x)) 0))] > > [x ix (+ x dx)] > > [y iy (+ y dy)] > > [c 0 (add1 c)]) > > ((= c 4) p))) > > > > I realize I've hard-coded this in a very ugly fashion to 20x20 vectors. > > > > My questions are: > > > > 1) Is there a more Racket-idiomatic way to write the "do" loop above? > > 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! > > > > Thanks, > > -joe > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > >
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