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willnet/happynumbers.hs

Created August 20, 2012 12:54
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happynumbers.hs
-- http://www.rubyquiz.com/quiz93.html
import Data.Char
checkHappy :: Int -> Bool
checkHappy n = checkHappy' [n]
checkHappy' :: [Int] -> Bool
checkHappy' list
| firstInput == 1 = True
| firstInput == nextValue = False
| otherwise = checkHappy' (nextValue:list)
where firstInput = last list
nextValue = next $ head list
next :: Int -> Int
next = foldl1 (+) . map ((^2) . digitToInt) . show
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