Day 10: Hoof It
Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
- You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://topaz.github.io/paste/ if you prefer sending it through a URL
FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
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 < rsize, csize)' coords =: ($ grid) & #: uncoords =: ($ grid) & #. 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 & uphill1)) neighbors y' adjacency_of =: monad define edges =. ; (< @: 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 : '({ & leads_to_matrix) @: < x, y' trailheads =: I. data = 0 summits =: I. data = 9 scores =: trailheads leads_to"0/ summits result1 =: +/, 0 < scores result2 =: +/, scoresFor some reason the code appears to be HTML escaped (I’m using the web interface on https://lemmy.sdf.org/)
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.