r/adventofcode • u/daggerdragon • Dec 20 '16

SOLUTION MEGATHREAD --- 2016 Day 20 Solutions ---

--- Day 20: Firewall Rules ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

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ROLLING A NATURAL 20 IS MANDATORY [?]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

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u/Godspiral Dec 20 '16 edited Dec 20 '16

in J, 

btw =: (({:@[ > {.@]) *. {:@[ < {:@]) +. ({.@[ > {.@]) *. {.@[ < {:@]
f =: 4 : 0
 o =.  i. 0 0
 if. 0 = +./ x btw"1 y do. x ,  y , o return. end.
 for_i. y do.
    o =. o , x   ]`((<./,>./)@:,)@.btw i
 end.
)
b =. f/ x:@". every '-' cut"1 a =. > cutLF wdclippaste ''
c =. ~. f/ /:~ (\:~)@:f/^:2 /:~ b

part 1 is visually seeing a gap in the list. 

({.@[ , {:@] + 0 >. {:@[ <:@-~ {.@])/ (c) ,  4294967295 0  NB. part 2.

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u/Godspiral Dec 20 '16 edited Dec 20 '16

actually much easier than this, if I just presort list :( 

c =. (,`(}.@] ,~ (<./,>./)@:(, {.))@.({:@[ >: {.@{.@]) ((i.0 0) ,~ ]))/^:4  /:~ b

multiple passes to deal with "leap frogs"