Challenge #119

changeCalc.hs

-- Types used
data Coin = Quarter | Dime | Nickle | Penny deriving (Show, Eq)
type CoinBag = [Coin]

-- variables
allCoins :: CoinBag
allCoins = [Quarter,Dime,Nickle,Penny]

-- Pretty printing helper
pretty :: CoinBag -> IO ()
pretty bag = do
             mapM_ putOne allCoins
               where putOne = \coin -> prettyLine coin (countCoins bag coin)

prettyLine :: Coin -> Int -> IO () 
prettyLine coin 0 = return () 
prettyLine coin count = putStrLn $ show coin ++ ": " ++ show count

countCoins :: CoinBag -> Coin -> Int
countCoins bag coin = length $ filter (== coin) bag 

-- Determine the value of a Coin or CoinBag
val :: Coin -> Integer 
val coin = case coin of
    Quarter -> 25
    Dime    -> 10
    Nickle  -> 5
    Penny   -> 1

bagVal :: CoinBag -> Integer
bagVal [] = 0
bagVal bag = sum $ map val bag

-- Algorithm for determining coins needed
addCoins :: CoinBag -> Integer -> Coin -> CoinBag
addCoins bag maxVal coin = 
    let potentialBag = coin:bag
    in if bagVal potentialBag > maxVal
       then bag
       else addCoins potentialBag maxVal coin

addAllCoins :: CoinBag -> Integer -> CoinBag -> CoinBag
addAllCoins bag maxVal [] = undefined
addAllCoins bag maxVal (coin:otherCoins) =    
    if bagVal bagWithC == maxVal
    then bagWithC
    else addAllCoins bagWithC maxVal otherCoins
      where bagWithC = addCoins bag maxVal coin

-- Helper for reading a Double value and converting to an Integer
getInteger :: IO Integer
getInteger = getLine >>= \x -> return . truncate . (100*) $ (read x :: Double)

-- Main method
main :: IO ()
main = do
       putStrLn "Enter a value:"
       amount <- getInteger
       pretty $ addAllCoins [] amount allCoins