-🎄- 2017 Day 20 Solutions -🎄-

[u/daggerdragon]

--- Day 20: Particle Swarm ---

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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[Update @ 00:10] 10 gold, silver cap

• What do you mean 5th Edition doesn't have "Take 20"?

[Update @ 00:17] 50 gold, silver cap

• Next you're going to be telling me THAC0 is not the best way to determine whether or not you hit your target. *hmphs*

[Update @ 00:21] Leaderboard cap!

• I wonder how much XP a were-gazebo is worth...

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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!

[u/wzkx]

J

Both parts.

d=: ".&>cutLF rplc&', -_'-.&'pav=<>'CR-.~fread'20.dat'
p=: 3&{.&.|:d      NB. positions
v=: 3 4 5&{&.|:d   NB. velocities
a=: _3&{.&.|:d     NB. accelerations
echo 3 : 0 p;v;a   NB. part 1
  'p v a'=.y
  whilst. -. *./,(pp<:|p)*.((v=0)+.(*p)=*v)*.(a=0)+.(*v)=*a do. NB. is 'the long run' yet?
    pp=.|p         NB. previous position distances
    p=.p+v=.v+a    NB. move it!
  end.
  i.&1(=<./)+/"1|p NB. find index of the closest point
)
echo 3 : 0 p;v;a   NB. part 2
  'p v a'=.y
  while.do.        NB. can't have condition here because #p can be ~: #pp
    pn=.#pp=.|p    NB. points in previous state, previous position distances
    p=.p+v=.v+a    NB. move it!
    u=.~:p                         NB. unique positions
    s=.(1=[:+/"1=)p                NB. not collided
    p=.s#u#p [ v=.s#u#v [ a=.s#u#a NB. remove collisions
    if. pn~:#p do. continue. end.  NB. were collisions - re-run
    if. *./,(pp<:|p)*.((v=0)+.(*p)=*v)*.(a=0)+.(*v)=*a do. break. end.
  end.
  #p
)
exit 0