Solved day 1 part 1

Main.hs

@@ -1,28 +1,57 @@
 module Main where
 
-import Data.List hiding (permutations)
-import Data.Set (Set)
-import qualified Data.Set as Set
-import qualified Data.Text.IO as TIO
+import Control.Applicative
 import qualified Data.Text as T
-import Data.Text.Read
+import qualified Data.Text.IO as TIO
+import qualified Data.Text.Read as TR
+import Data.Attoparsec.Text
 
 main :: IO ()
 main = do
     inputs <- TIO.readFile "input.txt"
-    let inputs' = T.lines inputs
-    let xs = map text2decimal inputs'
+    let Just entries = maybeResult $ parse entriesParser inputs
+    TIO.putStrLn $ T.pack $ show $ sum $ entries2ints entries
+
+data Entry = Entry
+  { policy :: Policy
+  , password :: String
+  } deriving (Show,Read)
+
+data Policy = Policy
+  { lowest :: Int
+  , highest :: Int
+  , character :: Char
+  } deriving (Show, Read)
+
+policyParser :: Parser Policy
+policyParser = do
+    low <- many digit
+    string "-"
+    high <- many digit
+    space
+    character <- letter
+    let Right (lowest, _) = TR.decimal $ T.pack low
+    let Right (highest, _) = TR.decimal $ T.pack high
+    return Policy { lowest = lowest, highest = highest, character = character }
 
-    let answer = calculateAnswer xs
+entryParser :: Parser Entry
+entryParser = do
+    policy <- policyParser
+    char ':'
+    space
+    password <- many letter
+    endOfLine
+    return Entry { policy = policy, password = password }
 
-    putStrLn $ show (answer :: Int)
+checkEntry :: Entry -> Bool
+checkEntry e = let p = policy e
+                   n = length $ filter ((character p) ==) (password e)
+               in n >= (lowest p) && n <= (highest p)
 
-text2decimal :: T.Text -> Int
-text2decimal t = case decimal t of
-                   Right(x, _) -> x
-                   Left(e) -> 0
+entriesParser :: Parser [Entry]
+entriesParser = do
+    entries <- many entryParser
+    return entries
 
-calculateAnswer :: [Int] -> Int
-calculateAnswer xs = answer $ head [ (x,y,z) | x <- xs, y <- xs, z <- xs, x+y+z==2020 ]
-  where
-      answer (a,b,c) = a * b * c
+entries2ints :: [Entry] -> [Int]
+entries2ints es = map (\e -> if checkEntry e then 1 else 0) es

advent-of-code.cabal

@@ -20,8 +20,9 @@ executable advent-of-code
   main-is: Main.hs
   other-modules:
       Paths_advent_of_code
+  default-extensions: OverloadedStrings
   build-depends:
-      base
-    , containers
+      attoparsec
+    , base
     , text
   default-language: Haskell2010

package.yaml

@@ -7,10 +7,13 @@ license: MIT
 build-type: Simple
 git: "https://git.bytes.zone/sehqlr/advent-of-code"
 
+default-extensions:
+    - OverloadedStrings
+
 dependencies:
     - base
-    - containers
     - text
+    - attoparsec
 
 executable:
     main: Main.hs