A-M baby

Task/Hailstone-sequence/Haskell/hailstone-sequence.hs

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+import Data.List (maximumBy)
+import Data.Ord (comparing)
+
+hailstone :: Int -> [Int]
+hailstone 1             = [1]
+hailstone n | even n    = n : hailstone (n `div` 2)
+            | otherwise = n : hailstone (n * 3 + 1)
+
+withResult :: (t -> t1) -> t -> (t1, t)
+withResult f x = (f x, x)
+
+main :: IO ()
+main = do
+ let h27 = hailstone 27
+ print $ length h27
+ let h4 = show $ take 4 h27
+ let t4 = show $ drop (length h27 - 4) h27
+ putStrLn ("hailstone 27: " ++ h4 ++ " ... " ++ t4)
+ print $ maximumBy (comparing fst) $ map (withResult (length . hailstone)) [1..100000]