40 lines
1.4 KiB
Haskell
40 lines
1.4 KiB
Haskell
import Data.Char (digitToInt)
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import qualified Data.Map as Map
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digitFactorial :: Integer -> Integer
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digitFactorial n = case n of
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0 -> 1
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1 -> 1
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2 -> 2
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3 -> 6
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4 -> 24
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5 -> 120
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6 -> 720
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7 -> 5040
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8 -> 40320
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9 -> 362880
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type ChainMap = Map.Map Integer Integer
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initialMap :: ChainMap
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initialMap = Map.fromList [(169, 3), (363601, 3), (1454, 3),
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(871, 2), (872, 2), (45361, 2), (45362, 2),
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(1, 1), (2, 1), (145, 1)]
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sumOfFactorialOfDigits :: Integer -> Integer
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sumOfFactorialOfDigits n = sum $ map (digitFactorial . fromIntegral . digitToInt) $ show n
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getChainLength :: Integer -> ChainMap -> (Integer, ChainMap)
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getChainLength n chainMap = case Map.lookup n chainMap of
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Just length -> (length, chainMap)
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Nothing -> let next = sumOfFactorialOfDigits n
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(nextLength, nextChainMap) = getChainLength next chainMap
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length = nextLength + 1
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in (length, Map.insert n length nextChainMap)
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numOfLoops :: Integer -> Integer -> (Integer, ChainMap)
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numOfLoops bound length = foldr (\n (num, oldMap) -> let (chainLength, newMap) = getChainLength n oldMap
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in (num + if chainLength == length then 1 else 0, newMap)) (0, initialMap) [3..bound]
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main = print $ let (length, sizeMap) = numOfLoops 10000 60
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in length
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