Maybe this?
>:@{. \: @:(] % totient)1+i.1000000
http://www.jsoftware.com/help/dictionary/d432.htm
or slightly more novice (me too!) friendly:
http://www.jsoftware.com/jwiki/Vocabulary/slashco
On Thu, Jun 12, 2014 at 1:37 AM, Jon Hough <[email protected]> wrote:
> Another Project Euler...
>
> This time PE #69: http://projecteuler.net/problem=69
>
> Essentially, find n which has the maximum of n/totient(n), for all
> positive integers, n, up to 1000000.
>
> At first this seemed easy. I have a verb to calculate the ratio:
> totient=: (- ~:)&.q:
> func =. ] % totient
> then I can find the maximum:
> max=. (>./)"1@:((] % totient)"0)
>
> max 1+i.1000000
> 5.53939
> But this gives me the ratio. I need to find n.
> This is a problem, because finding the maximum, the verb, >./ , collapsed
> the array so I don't think I can use I. or similar verb to get the index
> which gave the maximum ratio. So I am not sure how to find the n which gave
> this ratio.
>
> A second issue is I think my method seems to not be well thought out
> memory-wise. My method first calculates the ratio for every integer up to 1
> million and holds them all in memory. Surely a better way would be to do
> them one at a time and find the maximum as we go.
> In J I am not sure how to do this. I am guessing the recursion verb $:
> will need to be used.
> Any help appreciated.
> Regards.
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