Day 3

Day3.hs

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+module Day3 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.List ( maximumBy, minimumBy, group, sort )
+import Data.Function (on)
+import Data.Char (digitToInt)
+
+column :: String -> Int -> String
+column str i = map (!! i) $ lines str
+
+columns :: String -> Int
+columns str = maximum $ map length $ lines str
+
+mostCommon :: String -> Char
+mostCommon str = head . maximumBy (compare `on` length) . group $ sort str
+
+leastCommon :: String -> Char
+leastCommon str = head . minimumBy (compare `on` length) . group $ sort str
+
+binaryToDecimal :: Int -> Int
+binaryToDecimal = foldl1 ((+) . (2 *)) . map digitToInt . show
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/3.txt" ReadMode
+    contents <- hGetContents input
+
+    let gamma = mostCommon . column contents <$> [0..(columns contents - 1)]
+    let epsilon = leastCommon . column contents <$> [0..(columns contents - 1)]
+
+    let energy = product (binaryToDecimal . read <$> [gamma, epsilon] :: [Int])
+
+    print energy
+
+    hClose input

Day3_1.hs

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+module Day3_1 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.List ( maximumBy, minimumBy, group, sort )
+import Data.Function (on)
+import Data.Char (digitToInt)
+
+column :: [String] -> Int -> String
+column str i = map (!! i) str
+
+mostCommon :: String -> Char
+mostCommon str = head . maximumBy (compare `on` length) . group $ sort str
+
+leastCommon :: String -> Char
+leastCommon str = head . minimumBy (compare `on` length) . group $ sort str
+
+-- in: input strings, sorting method, current digit
+-- out: filtered strings
+filterColumns :: [String] -> (String -> Char) -> Int -> [String]
+filterColumns str sort i = filter (\a -> (a !! i) == commonChar) str
+    where
+        commonChar = sort $ column str i
+
+-- in: input strings, sorting method, current digit
+-- out: final rating
+rating :: [String] -> (String -> Char) -> Int -> String
+rating [str] _ _ = str
+rating str sort i = rating (filterColumns str sort i) sort (i+1)
+
+
+binaryToDecimal :: Int -> Int
+binaryToDecimal = foldl1 ((+) . (2 *)) . map digitToInt . show
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/3.txt" ReadMode
+    contents <- hGetContents input
+
+    let oxygen = rating (lines contents) mostCommon 0
+    let co2 = rating (lines contents) leastCommon 0
+
+    let rating = product (binaryToDecimal . read <$> [oxygen, co2] :: [Int])
+
+    print rating
+
+    hClose input