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I don't know about ya'll but Kotlin's `.toSortedMap().values` was very helpful in Part 2 for me.

I reused some code from Day 15: Rambunctious Recitation to find the specific allergen -&gt; ingredient mapping for  Part 2.  Might need to put that into a utility file for future years :slightly_smiling_face:

<https://github.com/ephemient/aoc2020/blob/main/kt/src/main/kotlin/io/github/ephemient/aoc2020/Day21.kt> also Grouping is fancy

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Indeed. When I first read it I was like "YES!"

For a brief moment in part 2, after the code ran I didn't reduce the possibilities for the allergens to 1 ingredient each, and I was like "aha, today I'll have to actually do search/backtracking"

and then it turned out that I forgot to actually propagate the trivial constraint as I looped through and found allergens that already had one possibility

And so... yeah it was very trivial. The difficulty curve on these is super uneven.

<http://www.maurits.vdschee.nl/scatterplot/> the difficulty curve this year seems very low overall, although this chart is also affected by the record number of participants

I think it's been easier too. Maybe Eric's giving us a break due to the current world situation? I'm still haunted by the terror of the water-filling simulation problem.

ah, I was only doing 3 languages that year :smile: I liked that puzzle

<https://github.com/ephemient/aoc2018/blob/kotlin/src/main/kotlin/io/github/ephemient/aoc2018/Day17.kt> not too bad, only ~100 lines

Blog: <https://todd.ginsberg.com/post/advent-of-code/2020/day21/>

Code: <https://github.com/tginsberg/advent-2020-kotlin/blob/main/src/main/kotlin/com/ginsberg/advent2020/Day21.kt>

Basically a lot of set manipulation. :slightly_smiling_face:

I keep getting surprised that these problems involving constraints, IIRC, have not required actual search/backtracking a single time yet

I do like that he puts the harder problems on the weekends. And so far, this year seems a lot easier than last year. There were a couple last year that I really struggled with.

I spent a most of it on part 1, part2 took me one line and maybe 10-15 seconds to find

<https://github.com/bjonnh/advent_of_code/blob/master/src/main/kotlin/y2020/day21/main.kt>

That's my raw output, didn't try to clean yet