2015 Day 09 in Haskell
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2015/day09/day09.hs
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28
2015/day09/day09.hs
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import Aoc
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import Data.List ( nub )
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import Data.Tuple ( swap )
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import Control.Applicative ( (<|>) )
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import Data.Maybe ( fromMaybe )
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parseFile :: [String] -> [((String, String), Int)]
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parseFile = map (\line ->
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let [a, "to", b, "=", dist] = words line in
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((a, b), read dist))
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symLookup :: Eq a => (a, a) -> [((a,a), b)] -> Maybe b
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symLookup a ls = lookup a ls <|> lookup (swap a) ls
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process :: [((String, String), Int)] -> [Int]
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process connections = map (totalLength . adjacents) (permutations cities)
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where
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cities = nub $ concatMap (unpair . fst) connections
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totalLength = sum . map (fromMaybe undefined . (`symLookup` connections))
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part1 :: [Int] -> Int
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part1 = minimum
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part2 :: [Int] -> Int
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part2 = maximum
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main = aocMain (process . parseFile) part1 part2
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17
aoc.hs
17
aoc.hs
@ -19,7 +19,7 @@ const' :: (a -> b) -> a -> c -> b
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const' f a _ = f a
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const' f a _ = f a
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enumerate :: [a] -> [(Int, a)]
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enumerate :: [a] -> [(Int, a)]
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enumerate xs = zip [0..length xs] xs
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enumerate = zip [0..]
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unimplemented :: Show p => p -> Int
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unimplemented :: Show p => p -> Int
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unimplemented = error . show
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unimplemented = error . show
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@ -27,6 +27,9 @@ unimplemented = error . show
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pair :: [a] -> (a, a)
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pair :: [a] -> (a, a)
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pair as = let [a1, a2] = as in (a1, a2)
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pair as = let [a1, a2] = as in (a1, a2)
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unpair :: (a, a) -> [a]
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unpair (a, b) = [a, b]
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triplet :: [a] -> (a, a, a)
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triplet :: [a] -> (a, a, a)
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triplet as = let [a1, a2, a3] = as in (a1, a2, a3)
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triplet as = let [a1, a2, a3] = as in (a1, a2, a3)
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@ -37,4 +40,14 @@ both :: (a -> b) -> (a, a) -> (b, b)
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both f (a, b) = (f a, f b)
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both f (a, b) = (f a, f b)
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lastSplit :: Int -> [a] -> ([a], [a])
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lastSplit :: Int -> [a] -> ([a], [a])
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lastSplit n as = splitAt (length as - n) as
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lastSplit n as = splitAt (length as - n) as
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remove :: Int -> [a] -> (a, [a])
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remove n xs = let (front, a:rest) = splitAt n xs in (a, front ++ rest)
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permutations :: [a] -> [[a]]
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permutations [] = [[]]
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permutations xs = concatMap (\n -> let (a, rest) = remove n xs in map (a:) $ permutations rest) [0..length xs-1]
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adjacents :: [a] -> [(a, a)]
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adjacents as = zip as $ tail as
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