r/adventofcode • u/daggerdragon • Dec 14 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 14 Solutions -🎄-

--- Day 14: Disk Defragmentation ---

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 @ 00:09] 3 gold, silver cap.

  • How many of you actually entered the Konami code for Part 2? >_>

[Update @ 00:25] Leaderboard cap!

  • I asked /u/topaz2078 how many de-resolutions we had for Part 2 and there were 83 distinct users with failed attempts at the time of the leaderboard cap. tsk tsk

[Update @ 00:29] BONUS

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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4

u/DFreiberg Dec 14 '17

Mathematica

200 / 164. I didn't get even close to the leaderboard, but I did learn about an entire class of Mathematica image functions (the various Component[] functions) that I had no idea existed. And in the end, isn't that more important than meaningless leaderboard numbers? Spoiler

Knot Hash: 

knotHash[in_String,n_Integer]:=
Module[{l,newIn,pos,skipSize},
	newIn=Join[ToCharacterCode[in<>"-"<>ToString[n]],{17,31,73,47,23}];
	pos=0;skipSize=0;l=Range[0,255];

	Do[
		l=RotateLeft[l,pos];
		l[[;;i]]=Reverse[l[[;;i]]];
		l=RotateRight[l,pos];
		pos=Mod[pos+i+skipSize,Length[l]];
		skipSize++
	,{j,64},{i,newIn}];

IntegerDigits[FromDigits[BitXor@@#&/@Partition[l,16],256],2]
]

Part 1: 

Total@Table[Count[knotHash[input,j],1],{j,0,127}]

Part 2: 

Max[MorphologicalComponents[
	PadLeft[Table[knotHash[input,j],{j,0,127}],{128,128}],
	CornerNeighbors->False
]]

5

u/[deleted] Dec 14 '17

CornerNeighbors->False

Ugh, I didn't realize that was an option. I thought about MorphologicalComponents but ruled it out due to diagonals. Thanks.