2020 day10/haskell: add solution

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Xiretza 2020-12-13 13:01:00 +01:00
parent 3645cd1985
commit 47c6817eab
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@ -15,6 +15,7 @@ https://adventofcode.com/2020/
| 7 | `**` | | |
| 8 | | `**` | |
| 9 | | `**` | |
|10 | | `**` | |
|11 | `**` | | |
`test.sh` can be used to run all solutions and automatically compares them to (my) puzzle inputs and the expected outputs.

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1885
2024782584832

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import AoC
import Data.List
pairs :: [a] -> [(a, a)]
pairs xs = zipWith (,) xs (tail xs)
part1 :: [Int] -> Int
part1 = product . map length . group . sort . map (uncurry $ flip (-)) . pairs
numArrangements :: [Int] -> Int
numArrangements = snd . head . go
where go xs = foldr (\x acc -> (x, sum . map snd . takeWhile (\(y, _) -> x-y <= 3) $ acc) : acc) [(last xs, 1)] $ init xs
main = runAoC (addPhonePort . sortReverse . (0:) . map read . lines) part1 numArrangements
where addPhonePort (x:xs) = (x+3):x:xs
sortReverse = sortBy (flip compare)