70 lines
1.7 KiB
Haskell
70 lines
1.7 KiB
Haskell
module Day8 where
|
|
|
|
import Data.Array
|
|
import Data.Char
|
|
import qualified Data.Set as S
|
|
import Text.ParserCombinators.ReadP
|
|
|
|
signedInt :: ReadP Int
|
|
signedInt = do
|
|
sign <- char '+' <++ char '-'
|
|
digits <- munch1 isDigit
|
|
return $ value sign digits
|
|
where
|
|
value '+' = read
|
|
value '-' = negate . read
|
|
|
|
data Inst = Acc Int | Jmp Int | Nop Int
|
|
deriving (Show)
|
|
|
|
inst :: ReadP Inst
|
|
inst = do
|
|
op <- choice $ map string ["acc", "jmp", "nop"]
|
|
_ <- skipSpaces
|
|
arg <- signedInt
|
|
return $ case op of
|
|
"acc" -> Acc arg
|
|
"jmp" -> Jmp arg
|
|
"nop" -> Nop arg
|
|
|
|
type Program = Array Int Inst
|
|
|
|
program :: ReadP Program
|
|
program = do
|
|
insts <- inst `sepBy` char '\n'
|
|
_ <- skipSpaces
|
|
_ <- eof
|
|
let bnds = (0, length insts - 1)
|
|
return $ listArray bnds insts
|
|
|
|
parse p s = unwrap $ readP_to_S p s
|
|
where
|
|
unwrap [(a, "")] = a
|
|
unwrap [(_, rs)] = error "Parser did not consume entire stream."
|
|
unwrap (a:as) = unwrap as
|
|
unwrap _ = error "Parser error"
|
|
|
|
data State = State { acc :: Int, sp :: Int, visits :: S.Set Int, looped :: Bool }
|
|
deriving (Show)
|
|
|
|
start = State 0 0 S.empty False
|
|
|
|
outOfBounds arr idx = idx < l || idx > r
|
|
where (l, r) = bounds arr
|
|
|
|
run pgrm = run' pgrm start
|
|
|
|
run' pgrm state
|
|
| outOfBounds pgrm $ sp state = state
|
|
| S.member (sp state) (visits state) = State (acc state) (sp state) (visits state) True
|
|
| otherwise = run' pgrm state'
|
|
where
|
|
state' = State acc' sp' visits' False
|
|
inst = pgrm ! (sp state)
|
|
acc' = case inst of
|
|
(Acc arg) -> (acc state + arg)
|
|
_ -> acc state
|
|
sp' = case inst of
|
|
(Jmp arg) -> (sp state + arg)
|
|
_ -> (sp state + 1)
|
|
visits' = S.insert (sp state) (visits state)
|