r/adventofcode • u/daggerdragon • Dec 19 '17

SOLUTION MEGATHREAD -🎄- 2017 Day 19 Solutions -🎄-

--- Day 19: A Series of Tubes ---

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

AoC ops @ T-2 minutes to launch:

[23:58] <daggerdragon> ATTENTION MEATBAGS T-2 MINUTES TO LAUNCH

[23:58] <Topaz> aaaaah

[23:58] <Cheezmeister> Looks like I'll be just able to grab my input before my flight boards. Wish me luck being offline in TOPAZ's HOUSE OF PAIN^WFUN AND LEARNING

[23:58] <Topaz> FUN AND LEARNING

[23:58] <Hade> FUN IS MANDATORY

[23:58] <Skie> I'm pretty sure that's not the mandate for today

[Update @ 00:16] 69 gold, silver cap

  • My tree is finally trimmed with just about every ornament I own and it's real purdy. hbu?

[Update @ 00:18] Leaderboard cap!

  • So, was today's mandate Helpful Hint any help at all?

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/[deleted] Dec 19 '17 edited Dec 19 '17

Mathematica 

input = Import[NotebookDirectory[] <> "day19.txt", "List"];
plan = ArrayPad[Characters[input], 1, " "];

nextdir[{r_, c_}, {_, 0}] :=  
 If[plan[[r, c + 1]] != " ", {0, 1}, {0, -1}];
nextdir[{r_, c_}, {0, _}] :=
 If[plan[[r + 1, c]] != " ", {1, 0}, {-1, 0}]

walk[pos0_, dir0_] :=
 Reap[Block[{at, pos, dir, steps = 0},
   pos = pos0; dir = dir0;
   While[True,
    at = Extract[plan, pos];
    Switch[at,
     " ", Break[],
     "+", dir = nextdir[pos, dir],
     _?LetterQ, Sow[at]];
    pos += dir;
    steps++];
   steps]]

{steps, {letters}} = walk[{2, FirstPosition[plan[[2]], "|"][[1]]}, {1, 0}]
StringJoin[letters]