Day 8

Day8.hs

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+module Day8 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.Text (splitOn, unpack, pack)
+import Prelude hiding (splitAt)
+
+splitAt :: String -> String -> [String]
+splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/8.txt" ReadMode
+    contents <- hGetContents input
+
+    let patterns = map (splitAt " ") . splitAt " | " <$> lines contents
+
+    print . sum . map (length . filter (\x -> length x `elem` [2,3,4,7])) $ (!! 1) <$> patterns
+
+    hClose input

Day8_1.hs

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+module Day8_1 where
+import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
+import Data.Text (splitOn, unpack, pack)
+import Prelude hiding (splitAt)
+import Data.List (sort, (\\))
+
+splitAt :: String -> String -> [String]
+splitAt delimiter str = map unpack $ splitOn (pack delimiter) $ pack str
+
+decode :: [String] -> [(String, Int)]
+decode nums = zip (head <$> [zero, one, two, three, four, five, six, seven, eight, nine]) [0..9]
+    where
+        one   = withLength 2
+        two   = filter (not . all (`elem` head nine)) $ withLength 5
+        three = withLength 5 \\ [head two, head five]
+        four  = withLength 4
+        five  = filter (all (`elem` head six)) $ withLength 5
+        six   = filter (\x -> not $ all (`elem` x) (head seven)) $ withLength 6
+        seven = withLength 3
+        eight = withLength 7
+        nine  = filter (\x -> all (`elem` x) (head four)) $ withLength 6
+        zero  = withLength 6 \\ [head nine, head six]
+        --
+        withLength y = filter ((== y) . length) nums
+
+decodeDigit :: [(String, Int)] -> String -> Int
+decodeDigit [] d = error "oh no"
+decodeDigit (x:xs) d
+    | fst x == d = snd x
+    | otherwise = decodeDigit xs d
+
+applyDecode :: [(String, Int)] -> [String] -> String
+applyDecode codes = concatMap (show . decodeDigit codes)
+
+main :: IO ()
+main = do
+    input <- openFile "inputs/8.txt" ReadMode
+    contents <- hGetContents input
+
+    let patterns = map (map sort . splitAt " ") . splitAt " | " <$> lines contents
+    let pairs = zip (head <$> patterns) ((!! 1) <$> patterns)
+
+    print $ sum (read <$> map (\x -> applyDecode (decode $ fst x) (snd x)) pairs :: [Int])
+
+    hClose input