Solution to the Round 1A of Google's Code Jam (http://goo.gl/yX6J8).

round_1a.hs

import Data.List.Split (splitOn)
import Control.Monad ((>=>))

newtype Circle = Circle { circleRadius :: Double }  deriving (Eq, Show)
newtype Paint  = Paint  { remainingMl :: Double }  deriving (Eq, Show)

data Ring = Ring { ringRadius       :: Double
                 , ringThickness    :: Double
                 } deriving (Eq, Show)

-- circle area
circleArea :: Circle -> Double
circleArea (Circle r) = (r ** 2) 

-- area of a ring
ringArea :: Ring -> Double
ringArea (Ring ra th) = (circleArea $ Circle ra) - (circleArea $ Circle (ra - th))

-- returns the next ring after the one passed
nextRing :: Ring -> Ring
nextRing (Ring r t) = Ring (r + t) t

-- with the given paint, tries to draw that ring and returns
-- the remaining paint or nothing
drawRing :: Paint -> Ring -> Maybe Paint
drawRing (Paint ml) r = if (rp >= 0) then Just (Paint rp) else Nothing
    where rp = ml - a
          a = ringArea r

-- returns the number of rings that can be drawn with 
-- that amount of paint and given that the next ring to draw is
-- the one given
ringsPerPaint :: Paint -> Ring -> Int -> Int
ringsPerPaint t r c = 
    case (drawRing t r) of
        Nothing -> 0
        Just p -> ringsPerPaint p nr (c + 1)
    where nr = (nextRing . nextRing) r

-- awaits for some input and process it into
-- a tuple of index, paint and starting ring
readInput :: Int -> IO (Int, Paint, Ring)
readInput i = do 
    ln <- getLine
    let ls = splitOn " " ln
        r = ((read $ head ls) :: Double)
        t = ((read $ last ls) :: Double)
    return (i, Paint t, Ring (r + 1) 1)

-- prints out the results
processOutput :: (Int, Paint, Ring) -> String
processOutput (i, p, r) = ("Case #" ++ (show i) ++ ": " ++ (show $ ringsPerPaint p r 0))
    
main :: IO ()
main = do
    gn <- getLine
    let n = (read gn :: Int)
    ls <- mapM (fmap processOutput . readInput) [1..n]
    mapM_ putStrLn ls