run.hs

{-# LANGUAGE TypeApplications #-}
import Data.Char (isDigit)
import Data.Bits (xor)
import Data.Ord (comparing)
import Data.Maybe
import Data.List
import Data.Sequence (Seq)
import qualified Data.Sequence as Seq
import Data.Set (Set)
import qualified Data.Set as Set

-- byr (Birth Year)
-- iyr (Issue Year)
-- eyr (Expiration Year)
-- hgt (Height)
-- hcl (Hair Color)
-- ecl (Eye Color)
-- pid (Passport ID)
-- cid (Country ID)

fields =
  [ "byr"
  , "iyr"
  , "eyr"
  , "hgt"
  , "hcl"
  , "ecl"
  , "pid"
  , "cid" ]

required = init fields

parseLineFields :: String -> [(String, String)]
parseLineFields =
  map parseLineField
  . words

parseLineField f =
  case span (/= ':') f of
    (fname, ':':value) -> (fname, value)

parse :: [String] -> [[(String, String)]]
parse = go [] Nothing
  where go acc (Just c) [] = reverse $ c:acc
        go acc curr (f:rest) =
          case (curr, parseLineFields f) of
            (Just c,  []) -> go (c:acc) Nothing rest
            (Nothing, []) -> go acc Nothing rest
            (Just c,  fs) -> go acc (Just (c ++ fs)) rest
            (Nothing, fs) -> go acc (Just fs) rest

parseAll =
  parse . lines

hasAllRequired pp = all (`elem` (map fst pp)) required

between v l h = l <= v && v <= h

validate "byr" v = between (read @Int v) 1920 2002
validate "iyr" v = between (read @Int v) 2010 2020
validate "eyr" v = between (read @Int v) 2020 2030
validate "hgt" v =
  case reads @Int v of
    [(v', "cm")] -> between v' 150 193
    [(v', "in")] -> between v' 59 76
    _ -> False
validate "hcl" ('#':v) = all (`elem` "0123456789abcdef") v
validate "ecl" v = v `elem` ["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]
validate "pid" v = length v == 9 && all isDigit v
validate "cid" _ = True
validate _ _ = False

-- byr (Birth Year) - four digits; at least 1920 and at most 2002.
-- iyr (Issue Year) - four digits; at least 2010 and at most 2020.
-- eyr (Expiration Year) - four digits; at least 2020 and at most 2030.
-- hgt (Height) - a number followed by either cm or in:

--     If cm, the number must be at least 150 and at most 193.
--     If in, the number must be at least 59 and at most 76.

-- hcl (Hair Color) - a # followed by exactly six characters 0-9 or a-f.
-- ecl (Eye Color) - exactly one of: amb blu brn gry grn hzl oth.
-- pid (Passport ID) - a nine-digit number, including leading zeroes.

valid pp = hasAllRequired pp && all (uncurry validate) pp

part1 = length . filter hasAllRequired
part2 = length . filter valid

main = do
   input <- parseAll <$> readFile "input.txt"
   print (part1 input)
   print (part2 input)