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- import Data.List (sort)
-
- main :: IO ()
- main = do
- raw <- readFile "day5.txt"
- let valid = foldr (&&) True $ map validate $ lines raw
- ls = if valid
- then map parse $ lines raw
- else error "invalid input"
- ansA = maximum ls
- ansB = findGap $ sort ls
- in do
- putStrLn $ "day5a: " ++ (show ansA)
- putStrLn $ "day5b: " ++ (show ansB)
-
- validate :: String -> Bool
- validate s =
- length s == 10
- && all (`elem` ['F', 'B']) (take 7 s)
- && all (`elem` ['L', 'R']) (drop 7 s)
-
- parse :: String -> Int
- parse s = row * 8 + column
- where
- rowString = (take 7 s)
- columnString = (drop 7 s)
- row = fromBinaryString 'B' rowString
- column = fromBinaryString 'R' columnString
-
- fromBinaryString :: Char -> String -> Int
- fromBinaryString t s =
- foldr (+) 0 $ map snd $ filter (\x -> fst x == t) $ zip (reverse s) powList
-
- findGap :: [Int] -> Int
- findGap [] = error "empty list"
- findGap [x] = error "short list"
- findGap (x:y:xs) =
- if y == succ x
- then findGap (y:xs)
- else succ x
-
- powList :: [Int]
- powList = 1 : map (* 2) powList
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