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day9: add haskell solution

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Xiretza 1 year ago
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Signed by: xiretza
GPG Key ID: 17B78226F7139993
  1. 1
      README.md
  2. 2
      data/day9.expected
  3. 1000
      data/day9.input
  4. 30
      day9/day9.hs

1
README.md

@ -14,5 +14,6 @@ https://adventofcode.com/2020/
| 6 | | `**` | |
| 7 | `**` | | |
| 8 | | `**` | |
| 9 | | `**` | |
`test.sh` can be used to run all solutions and automatically compares them to (my) puzzle inputs and the expected outputs.

2
data/day9.expected

@ -0,0 +1,2 @@
26134589
3535124

1000
data/day9.input

File diff suppressed because it is too large Load Diff

30
day9/day9.hs

@ -0,0 +1,30 @@
import AoC
import Control.Monad
import Data.List
import Data.Maybe
slidingWindow :: Int -> [a] -> [[a]]
slidingWindow n xs
| length xs < n = []
| otherwise = take n xs : slidingWindow n (tail xs)
summingTo :: (Eq a, Num a) => Int -> a -> [a] -> Maybe [a]
n `summingTo` x = find ((==x) . sum) . replicateM n
sublistSummingTo :: (Num a, Ord a) => a -> [a] -> Maybe [a]
sublistSummingTo n = fmap snd . find ((== n) . fst) . scanl go (0, [])
where go = dropNeeded .: addToAcc
addToAcc (sum, parts) x = (sum+x, parts++[x])
dropNeeded = fromJust . find ((<= n) . fst) . iterate dropPart
dropPart (sum, (x:xs)) = (sum-x, xs)
part1 :: [Int] -> Int
part1 = snd . fromJust . find (not . uncurry doesSum) . map (\xs -> (init xs, last xs)) . slidingWindow 26
where doesSum xs y = isJust $ 2 `summingTo` y $ xs
part2 :: [Int] -> Int
part2 xs = minimum range + maximum range
where range = fromJust $ sublistSummingTo (part1 xs) xs
main = runAoC (map read . lines) part1 part2
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