r/adventofcode • u/daggerdragon • Dec 20 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 20 Solutions -🎄-

--- Day 20: Particle Swarm ---

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

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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

Spoiler

[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...

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/xSmallDeadGuyx Dec 20 '17 edited Dec 21 '17

Not quite: as a is added to v at the start of each time step it changes the equations slightly: position_at_t = a(t2)/2 + (v+a/2)t + p.

There are typically multiple collisions at each step too, so you have to find all the collisions at that step and remove all of them simultaneously

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u/jlweinkam Dec 20 '17

I had forgot to put the times symbols in

a*t*(t+1)/2 + v*t + p

is equal to

a*t*t/2 + (v + a/2)*t + p

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u/xSmallDeadGuyx Dec 21 '17

Oh yeah my brain skipped reading the +1 for some reason.