Day 1

01/gold.hs

@@ -0,0 +1,35 @@
+
+import Data.List -- sort
+import Data.Map (Map)
+import qualified Data.Map.Strict as Map.Strict
+import qualified Data.Map as Map
+
+mapTuple :: (a -> b) -> (a, a) -> (b, b)
+mapTuple f (a1, a2) = (f a1, f a2)
+
+countH :: Ord a => Map a Integer -> [a] -> Map a Integer
+countH m (x:xs) = countH newmap xs
+    where newmap = Map.Strict.insertWith (+) x 1 m
+countH m _ = m
+
+count :: Ord a => [a] -> Map a Integer
+count = countH Map.empty
+
+applyToSecond :: (b->c) -> (a, b) -> (a, c) 
+applyToSecond f (x, y) = (x, f y)
+
+toColumnsH :: [a] -> [a] -> [a] -> ([a], [a])
+toColumnsH ls rs (x:xs) = toColumnsH rs (ls++[x]) xs
+toColumnsH ls rs _ = (ls, rs)
+
+toColumns :: [a] -> ([a], [a])
+toColumns = toColumnsH [] []
+
+similarityH :: Integer -> Map Integer Integer -> [Integer] -> Integer
+similarityH acc m (x:xs) = similarityH (acc + x * (Map.findWithDefault 0 x m)) m xs
+similarityH acc m _ = acc
+
+similarity :: ([Integer], Map Integer Integer) -> Integer
+similarity (xs, m) = similarityH 0 m xs
+
+main = interact $ show . similarity . applyToSecond count . mapTuple sort . toColumns . map read . words

01/silver.hs

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+
+import Data.List -- sort
+
+mapTuple :: (a -> b) -> (a, a) -> (b, b)
+mapTuple f (a1, a2) = (f a1, f a2)
+
+-- helper function for split
+splitH :: [a] -> [a] -> [a] -> ([a], [a])
+splitH ls rs (x:xs) = splitH rs (ls++[x]) xs
+splitH ls rs _ = (ls, rs)
+
+-- split: split list into two by alternating between left and right
+split :: [a] -> ([a], [a])
+split = splitH [] []
+
+-- calculates the sum of the absolute distance between two lists
+dist :: Int -> ([Int], [Int]) -> Int
+dist acc (l:ls, r:rs) = dist (acc + abs (r - l)) (ls, rs)
+dist acc _ = acc
+
+main = interact $ show . dist 0 . mapTuple sort . split . map (read :: String -> Int) . words

01/test.txt

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+5 6
+3 4
+1 2