Ruby Quiz, Haskell Solution: Happy Numbers
Posted: August 24th, 2009 | Author: Michel Rijnders | Filed under: Haskell, Ruby Quiz | No Comments »The Quiz
Write a program that tells whether a given integer is happy. A happy number is found using the following process: Take the sum of the squares of its digits, and continue iterating this process until it yields 1, or produces an infinite loop. (The complete, original quiz is here.)
A Haskell Solution
module Main where
import System (getArgs)
digits :: Int -> [Int]
digits = map (\c -> read [c] :: Int) . show
happy :: Int -> Bool
happy n = happy' n []
where
s = sum . map (\x -> x * x) . digits
happy' n ns
| s n == 1 = True
| s n `elem` ns = False
| otherwise = happy' (s n) (n : ns)
main :: IO ()
main = do
args <- getArgs
if happy (read (head args) :: Int)
then putStrLn ":-)"
else putStrLn ":-("
return ()
import System (getArgs)
digits :: Int -> [Int]
digits = map (\c -> read [c] :: Int) . show
happy :: Int -> Bool
happy n = happy' n []
where
s = sum . map (\x -> x * x) . digits
happy' n ns
| s n == 1 = True
| s n `elem` ns = False
| otherwise = happy' (s n) (n : ns)
main :: IO ()
main = do
args <- getArgs
if happy (read (head args) :: Int)
then putStrLn ":-)"
else putStrLn ":-("
return ()
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