81 lines
3.1 KiB
Markdown
81 lines
3.1 KiB
Markdown
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## \-\-- Day 13: Knights of the Dinner Table \-\--
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In years past, the holiday feast with your family hasn\'t gone so well.
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Not everyone gets along! This year, you resolve, will be different.
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You\'re going to find the *optimal seating arrangement* and avoid all
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those awkward conversations.
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You start by writing up a list of everyone invited and the amount their
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happiness would increase or decrease if they were to find themselves
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sitting next to each other person. You have a circular table that will
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be just big enough to fit everyone comfortably, and so each person will
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have exactly two neighbors.
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For example, suppose you have only four attendees planned, and you
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calculate
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their potential happiness as follows:
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Alice would gain 54 happiness units by sitting next to Bob.
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Alice would lose 79 happiness units by sitting next to Carol.
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Alice would lose 2 happiness units by sitting next to David.
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Bob would gain 83 happiness units by sitting next to Alice.
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Bob would lose 7 happiness units by sitting next to Carol.
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Bob would lose 63 happiness units by sitting next to David.
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Carol would lose 62 happiness units by sitting next to Alice.
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Carol would gain 60 happiness units by sitting next to Bob.
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Carol would gain 55 happiness units by sitting next to David.
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David would gain 46 happiness units by sitting next to Alice.
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David would lose 7 happiness units by sitting next to Bob.
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David would gain 41 happiness units by sitting next to Carol.
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Then, if you seat Alice next to David, Alice would lose `2` happiness
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units (because David talks so much), but David would gain `46` happiness
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units (because Alice is such a good listener), for a total change of
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`44`.
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If you continue around the table, you could then seat Bob next to Alice
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(Bob gains `83`, Alice gains `54`). Finally, seat Carol, who sits next
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to Bob (Carol gains `60`, Bob loses `7`) and David (Carol gains `55`,
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David gains `41`). The arrangement looks like this:
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+41 +46
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+55 David -2
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Carol Alice
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+60 Bob +54
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-7 +83
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After trying every other seating arrangement in this hypothetical
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scenario, you find that this one is the most optimal, with a total
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change in happiness of `330`.
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What is the *total change in happiness* for the optimal seating
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arrangement of the actual guest list?
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Your puzzle answer was `733`.
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## \-\-- Part Two \-\-- {#part2}
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In all the commotion, you realize that you forgot to seat yourself. At
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this point, you\'re pretty apathetic toward the whole thing, and your
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happiness wouldn\'t really go up or down regardless of who you sit next
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to. You assume everyone else would be just as ambivalent about sitting
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next to you, too.
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So, add yourself to the list, and give all happiness relationships that
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involve you a score of `0`.
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What is the *total change in happiness* for the optimal seating
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arrangement that actually includes yourself?
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Your puzzle answer was `725`.
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Both parts of this puzzle are complete! They provide two gold stars:
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\*\*
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At this point, you should [return to your Advent calendar](/2015) and
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try another puzzle.
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If you still want to see it, you can [get your puzzle
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input](13/input).
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