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module Ch2 where
import Data.List
digits :: Integral a => a -> [a]
digits 0 = []
digits x = digits (div x 10) ++ [mod x 10]
helper :: Integral a => a -> a -> a
helper acc n
| n < 10 = acc
| otherwise =
helper (acc+1) (product $ digits n)
persistenceSort :: Integral a => [a] -> [a]
persistenceSort xs =
sortBy (\a b -> let ha = helper 0 a; hb = helper 0 b in
if ha /= hb then
compare ha hb
else compare a b) xs
main :: IO ()
main = do
print $ persistenceSort [15,99,1,34]
print $ persistenceSort [50,25,33,22]
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