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import Data.Array
import Data.Ratio (denominator, numerator)
import Text.Parsec
type Matrix = Array (Int,Int) Rational
type Pair = (Rational,Rational)
det :: Matrix -> Rational
det m = a*d - b*c
where
a = m ! (1,1)
b = m ! (2,1)
c = m ! (1,2)
d = m ! (2,2)
matrix :: Pair -> Pair -> Matrix
matrix (a,c) (b,d) =
array ((1,1),(2,2)) [((1,1),a), ((2,1),b), ((1,2),c), ((2,2),d)]
solve :: Pair -> Pair -> Pair -> Pair
solve target a b = (solA, solB)
where
coefficients = matrix a b
solA = det (matrix target b) / det coefficients
solB = det (matrix a target) / det coefficients
int :: Rational -> Bool
int = (== 1) . denominator
maybeSolve :: Pair -> Pair -> Pair -> Maybe Pair
maybeSolve target a b =
let sol@(a',b') = solve target a b
in if int a' && int b'
then Just sol
else Nothing
cost :: Pair -> Pair -> Pair -> Int
cost target a b = case maybeSolve target a b of
Nothing -> 0
Just (a',b') -> fromIntegral . numerator $ 3*a' + b'
cost' :: (Pair,Pair,Pair) -> Int
cost' (a, b, target) = cost target a b
number :: Parsec String () Rational
number = fromInteger . read <$> many digit
button :: Parsec String () Pair
button = (,)
<$ string "Button "
<* anyChar
<* string ": X+"
<*> number
<* string ", Y+"
<*> number
<* newline
prize :: Parsec String () Pair
prize = (,)
<$ string "Prize: X="
<*> number
<* string ", Y="
<*> number
<* newline
parseOne :: Parsec String () (Pair,Pair,Pair)
parseOne = (,,) <$> button <*> button <*> prize
parseInput :: Parsec String () [(Pair,Pair,Pair)]
parseInput = sepBy parseOne newline
doParse :: String -> [(Pair,Pair,Pair)]
doParse s = case parse parseInput "" s of
Left e -> error $ show e
Right a -> a
main :: IO ()
main = getContents >>= print . sum . map cost' . doParse
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