My solution (after studying the previous solution):
NB. read file:
file =: fread < '~/p067_triangle.txt'
data =: cutopen file
result =: ":@:(".@:[ + 2&(>./\)@:".@:])&.>/ data
The standard library function cutopen splits the file into rows and boxes each
row. The final verb opens the x,y operands and gets the pairwise max of y and
adds it to x, while converting to integers. It's a bit clunky because I have to
switch it back to literal before reboxing it.
> From: [email protected]
> Date: Sat, 10 Jan 2015 17:56:20 -0500
> To: [email protected]
> Subject: Re: [Jprogramming] Dear Roger Hui!
>
> Yeah, I miscopied the code.
>
> The original had >. and I used +
>
> Same basic structure, but I never looked back to proofread my original
> expression.
>
> Also >. makes more sense than + in the context of that euler project.
>
> Thanks,
>
> --
> Raul
>
> On Sat, Jan 10, 2015 at 3:30 PM, Tikkanz <[email protected]> wrote:
> > Should that be "pairwise maximum" rather than "pairwise sum"?
> > On 10 Jan 2015 14:55, "Raul Miller" <[email protected]> wrote:
> >
> >> I guess I can do a low-level view of how the code works. Though I'm
> >> not going to use sample data from euler 67 - have to leave you
> >> something to do... instead, I'll use
> >>
> >> i.3 3
> >> 0 1 2
> >> 3 4 5
> >> 6 7 8
> >>
> >> as the sample data.
> >>
> >> So that's this:
> >> {. (+ 0: ,~ 2: >./\ ])/ i.3 3
> >> 12
> >>
> >> We also don't need : after the numbers, for this particular case, in
> >> modern versions of J, nor do we need the spaces, and I'm going to want
> >> this to be compact, in a moment, so:
> >> {. (+0,~2>./\])/ i.3 3
> >> 12
> >>
> >> Let's start breaking that down. First, let's remove the 'first' verb,
> >> so we see what it is acting on:
> >>
> >> (+0,~2>./\])/ i.3 3
> >> 12 13 2
> >>
> >> Now how did that happen? Well, in this case the / operator inserts its
> >> verb between the items of its noun. So, that is:
> >> 0 1 2 (+0,~2>./\]) 3 4 5 (+0,~2>./\]) 6 7 8
> >> 12 13 2
> >>
> >> Next, let's look at just one of these cases to see how it works:
> >>
> >> 3 4 5 (+0,~2>./\]) 6 7 8
> >> 10 12 5
> >>
> >> So how does that work? Well, if we count the verbs in (+0,~2>./\])
> >> there's an even number of them, so the top level structure is a hook.
> >> And, it's a dyadic hook (with an argument on its left), so that means
> >> we can just remove the parenthesis in that sentence (need to read the
> >> documentation on hooks, really - I'm oversimplifying the definitions
> >> for only their relevance in this case):
> >>
> >> 3 4 5 +0,~2>./\] 6 7 8
> >> 10 12 5
> >>
> >> In other words, it's 3 4 5 + the result of the rest of that stuff.
> >>
> >> So:
> >> 0,~2>./\] 6 7 8
> >> 7 8 0
> >>
> >> That's the pair-wise sum of the elements of the list, with a zero
> >> tacked onto the right hand side.
> >>
> >> Again, I'm oversimplifying things here - you should be able to perform
> >> your own experiments and/or read the definitions either in the
> >> official dictionary
> >> http://www.jsoftware.com/help/dictionary/vocabul.htm or in the
> >> unofficial nuvoc http://www.jsoftware.com/jwiki/NuVoc -- but be sure
> >> to try things out, some, to help resolve ambiguities and especially
> >> when you think you understand things (because sometimes things are
> >> surprising).
> >>
> >> So anyways, {. (+ 0: ,~ 2: >./\ ])/ m is, basically:
> >>
> >> The first thing from:
> >>
> >> adding each row to
> >> the pairwise sum of
> >> this result for the previous row
> >>
> >> (padding pairwise sums on the right, to keep things the same length)
> >>
> >> I hope this helps.
> >>
> >> Thanks,
> >>
> >> --
> >> Raul
> >>
> >> On Sat, Jan 10, 2015 at 1:06 PM, Roger Hui <[email protected]>
> >> wrote:
> >> > Hmm, I bet you a Java solution would be longer, eh? :-)
> >> >
> >> > It's been years since I solve Project Euler 67, and I am busy with other
> >> > things on the weekend, so there'll be a delay in a detailed description.
> >> > Probably others will chime in meanwhile.
> >> >
> >> >
> >> >
> >> > On Sat, Jan 10, 2015 at 9:58 AM, oventarb oventarb <[email protected]>
> >> > wrote:
> >> >
> >> >>
> >> >> Dear Roger Hui!
> >> >> I solved problem 67 using Java.
> >> >> What does this code mean:
> >> >>
> >> >> {. (+ 0: ,~ 2: >./\ ])/ m
> >> >> ----------------------------------------------------------------------
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> >> >>
> >> > ----------------------------------------------------------------------
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> >>
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