Day 10: Hoof It

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[-] ystael@beehaw.org 2 points 1 week ago* (last edited 1 week ago)

J

Who needs recursion or search algorithms? Over here in line noise array hell, we have built-in sparse matrices! :)

data_file_name =: '10.data'
grid =: "."0 ,. > cutopen fread data_file_name
data =: , grid
'rsize csize' =: $ grid
inbounds =: monad : '(*/ y >: 0 0) * (*/ y &lt; rsize, csize)'
coords =: ($ grid) &amp; #:
uncoords =: ($ grid) &amp; #.
NB. if n is the linear index of a point, neighbors n lists the linear indices
NB. of its orthogonally adjacent points
neighbors =: monad : 'uncoords (#~ inbounds"1) (coords y) +"1 (4 2 $ 1 0 0 1 _1 0 0 _1)'
uphill1 =: dyad : '1 = (y { data) - (x { data)'
uphill_neighbors =: monad : 'y ,. (#~ (y &amp; uphill1)) neighbors y'
adjacency_of =: monad define
   edges =. ; (&lt; @: uphill_neighbors"0) i.#y
   NB. must explicitly specify fill of integer 0, default is float
   1 edges} 1 $. ((#y), #y); (0 1); 0
)
adjacency =: adjacency_of data
NB. maximum path length is 9 so take 9th power of adjacency matrix
leads_to_matrix =: adjacency (+/ . *)^:8 adjacency
leads_to =: dyad : '({ &amp; leads_to_matrix) @: &lt; x, y'
trailheads =: I. data = 0
summits =: I. data = 9
scores =: trailheads leads_to"0/ summits
result1 =: +/, 0 &lt; scores
result2 =: +/, scores

[-] sjmulder@lemmy.sdf.org 2 points 1 week ago* (last edited 1 week ago)

For some reason the code appears to be HTML escaped (I'm using the web interface on https://lemmy.sdf.org)

[-] ystael@beehaw.org 2 points 1 week ago* (last edited 1 week ago)

Yes. I don't know whether this is a beehaw specific issue (that being my home instance) or a lemmy issue in general, but < and & are HTML escaped in all code blocks I see. Of course, this is substantially more painful for J code than many other languages.

this post was submitted on 10 Dec 2024

15 points (89.5% liked)

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