adventofcode-2021/3/diagnosticReader.hs

import           Control.Exception (assert)
import           Data.Bits         (bit)
import           Data.Char         (digitToInt)
import           Data.List         (group, intersect, maximumBy, minimumBy,
                                    sort, transpose)
import           Data.Ord          (comparing)

main :: IO ()
main = do
  diagnostics <- getContents
  putStrLn (solution1 diagnostics)
  putStrLn (solution2 diagnostics)

solution1 :: String -> String
solution1 diagnostics = show (calcGamma * calcEpsilon)
  where
    calcGamma = listToBit (map most (transpose (parseDiagnostics diagnostics)))
    calcEpsilon = listToBit (map least (transpose (parseDiagnostics diagnostics)))

solution2 :: String -> String
solution2 diagnostics = show (calcOxygen * calcCO2)
  where
    calcOxygen = listToBit (head (filterForLife most (parseDiagnostics diagnostics)))
    calcCO2 = listToBit (head (filterForLife least (parseDiagnostics diagnostics)))

parseDiagnostics :: String -> [[Int]]
parseDiagnostics diagnostics = map (map digitToInt) (lines diagnostics)

enumerate :: [a] -> [(Int, a)]
enumerate = zip [0..]

most :: [Int] -> Int
most = head . (maximumBy (comparing length)) . group . sort

least :: [Int] -> Int
least = head . (minimumBy (comparing length)) . group . sort

listToBit :: [Int] -> Int
listToBit list = foldr (\b acc -> (acc + toBit b)) 0 (enumerate (reverse list))
  where
    -- Takes a location and value to converts it to the appropriate
    -- integer.
    toBit :: (Int, Int) -> Int
    toBit (i, b) = if b == 1
                   then bit i
                   else 0

filterForLife :: ([Int] -> Int) -> [[Int]] -> [[Int]]
filterForLife targetFilter list = foldl (filterIndex targetFilter) list [0..length(head list)-1]

filterIndex :: ([Int] -> Int) -> [[Int]] -> Int -> [[Int]]
filterIndex targetFilter list index = filter ((==filterTarget) . (!! index)) list
  where
    filterTarget :: Int
    filterTarget = targetFilter ((transpose list) !! index)

-- Tests

testInput1 :: String
testInput1 = unlines [
  "00100",
  "11110",
  "10110",
  "10111",
  "10101",
  "01111",
  "00111",
  "11100",
  "10000",
  "11001",
  "00010",
  "01010"
  ]

test1 :: String
test1 = assert ((solution1 testInput1) == "198") "success"

test2 :: String
test2 = assert ((solution2 testInput1) == "230") "success"