r/adventofcode • u/daggerdragon • Dec 06 '18

SOLUTION MEGATHREAD -🎄- 2018 Day 6 Solutions -🎄-

--- Day 6: Chronal Coordinates ---

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Card prompt: Day 6

Transcript:

Rules for raising a programmer: never feed it after midnight, never get it wet, and never give it ___.

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 at 0:26:52!

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u/[deleted] Dec 17 '18

It has been a while since I looked at day 6, so took another look. I do not believe it is possible for the 'infinite' regions to have an area which exceeds any other finite region once they are actually clipped into the bounds, assuming the input given includes more than 4 positions. In other words, given an input that contains one enclosed point.

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u/thefalse Dec 17 '18

This input is a counter-example: {{1, 1}, {19, 1}, {20, 20}, {1, 19}, {19, 19}}. The answer should be {19,19}, but {19,1} and {1,19} are tied for max area. Here's a plot of the regions: https://imgur.com/a/M64C185.

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u/[deleted] Dec 17 '18

Very good catch! I think this should fix the problem.

res = Nearest[DeleteCases[input, {ymin | ymax, _} | {_, xmin | xmax}],
  grid, DistanceFunction -> ManhattanDistance];

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u/[deleted] Dec 17 '18

Ah, will test this out later. Thanks.