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day13: 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/day13.expected
  3. 2
      data/day13.input
  4. 47
      day13/day13.hs

1
README.md

@ -17,5 +17,6 @@ https://adventofcode.com/2020/
| 9 | | `**` | |
|10 | | `**` | |
|11 | `**` | | |
|13 | | `**` | |
`test.sh` can be used to run all solutions and automatically compares them to (my) puzzle inputs and the expected outputs.

2
data/day13.expected

@ -0,0 +1,2 @@
2215
1058443396696792

2
data/day13.input

@ -0,0 +1,2 @@
1005162
19,x,x,x,x,x,x,x,x,41,x,x,x,x,x,x,x,x,x,823,x,x,x,x,x,x,x,23,x,x,x,x,x,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,443,x,x,x,x,x,37,x,x,x,x,x,x,13

47
day13/day13.hs

@ -0,0 +1,47 @@
module Day13 where
import AoC
import Data.List
import Data.List.Split
import Data.Maybe
import Data.Ord
import Data.Tuple
-- | inverse integer modulus, "remainder until the next multiple of d"
--
-- @(n + n `'invMod'` d) `'mod'` d == 0@
invMod :: Integral a => a -> a -> a
invMod n d | r == 0 = 0
| otherwise = d - r
where r = n `mod` d
-- | @'combineRemainders' (r1, d1) (r2, d2) = (r3, d3)@ combines a relation of the form
--
-- @
-- x = r1 (mod d1)
-- x = r2 (mod d2)
-- @
--
-- into a single relation
--
-- @
-- x = r3 (mod d3)
-- @
--
-- @d1@ should be larger than @d2@ for better performance.
combineRemainders :: (Integral a) => (a, a) -> (a, a) -> (a, a)
combineRemainders (r1, d1) (r2, d2) = (fromJust . find (\x -> x `mod` d2 == r2) $ [r1,d1+r1..], d1*d2)
part1 :: Int -> [Int] -> Int
part1 arr = uncurry (*) . minimumBy (comparing snd) . map (toSnd $ invMod arr)
where toSnd f x = (x, f x)
part2 :: [Maybe Int] -> Int
part2 = fst . foldl1 combineRemainders . map (\(r, d) -> (r `invMod` d, d)) . catMaybes . map sequence . enumerate 0
where enumerate start (x:xs) = (start, x) : enumerate (succ start) xs
enumerate _ [] = []
main = runAoC (intoTuple . map (map (fmap read . justIf (/="x")) . splitOn ",") . lines) (uncurry part1 . fmap catMaybes) (part2 . snd)
where intoTuple [[Just x], y] = (x, y)
justIf p x = if p x then Just x else Nothing
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