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|
module Main where
import Data.Either (fromLeft, fromRight)
import Data.List (foldl', sort)
import Data.Map (Map, (!))
import qualified Data.Map as Map
import Utils
data Expr
= Paren [Expr]
| Bracket [Expr]
| Curly [Expr]
| Angle [Expr]
deriving (Show)
data Failure
= Incomplete
| Corrupted Char
deriving (Show)
type Computation a = Either Failure a
consume expected (c : cs) =
if c /= expected
then Left (Corrupted c)
else Right cs
consume expected [] = Left Incomplete
pairs =
Map.fromList
[ ('(', ')'),
('[', ']'),
('{', '}'),
('<', '>')
]
opening = Map.keys pairs
closing = Map.elems pairs
expr :: Char -> [Expr] -> Expr
expr '(' children = Paren children
expr '[' children = Bracket children
expr '{' children = Curly children
expr '<' children = Angle children
expr c _ = error $ "invalid c: " ++ [c]
parse :: String -> Computation ([Expr], String)
parse s
| null s = Left Incomplete
| head s `elem` opening =
let (c : cs) = s
closing = pairs ! c
in do
(children, rest) <- parse cs
rest' <- consume closing rest
(nextExprs, rest'') <-
if not (null rest')
then parse rest'
else Right ([], rest')
Right (expr c children : nextExprs, rest'')
| head s `elem` closing = Right ([], s)
| otherwise = error "unreachable"
isCorrupted expr = case expr of
Left (Corrupted c) -> True
_ -> False
fromCorrupted expr = case expr of
Left (Corrupted c) -> c
a -> error $ "not corrupted: " ++ show a
score1 ')' = 3
score1 ']' = 57
score1 '}' = 1197
score1 '>' = 25137
score1 a = error $ "not valid for scoring: " ++ [a]
e1 rows =
let parsed = map parse rows
corrupted = parsed $> filter isCorrupted .> map fromCorrupted
scores = corrupted $> map score1
in sum scores
repair :: [Char] -> [Char] -> Either Failure [Char]
repair expectStack s
| null s = Right expectStack
| head s `elem` opening =
let (c : cs) = s
correspondingClosing = pairs ! c
expectStack' = correspondingClosing : expectStack
in repair expectStack' cs
| head s `elem` closing =
do
let (c : cs) = s
let (ec : ecs) = expectStack
if c /= ec
then Left (Corrupted c)
else repair ecs cs
| otherwise = error "unreachable"
score2 ')' = 1
score2 ']' = 2
score2 '}' = 3
score2 '>' = 4
score2 a = error $ "not valid for scoring: " ++ [a]
fixToScore = foldl' (\acc c -> 5 * acc + score2 c) 0
e2 rows =
let parsed = map (repair []) rows
fixesM = parsed $> filter (not . isCorrupted)
fixes = fixesM $> map (\(Right fix) -> fix)
scores = fixes $> map fixToScore
scoresSorted = sort scores
scoresN = length scoresSorted
in scoresSorted !! (scoresN `div` 2)
main :: IO ()
main =
do
contents <- getContents
let input = contents $> lines
e1 input $> print
e2 input $> print
|
