42 lines
1.1 KiB
Haskell
42 lines
1.1 KiB
Haskell
import Data.Char (digitToInt)
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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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sizeOfLoop :: Integer -> Integer
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sizeOfLoop n
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| n == 169 || n == 363601 || n == 1454 = 3
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| n == 871 || n == 45361 = 2
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| n == 872 || n == 45362 = 2
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| n == 145 || n == 1 || n == 2 = 1
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| otherwise = 0
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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 -> Integer
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getChainLength n = getChainLengthRec n 1
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getChainLengthRec :: Integer -> Integer -> Integer
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getChainLengthRec n length =
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let next = sumOfFactorialOfDigits n
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nextLength = sizeOfLoop next
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in if nextLength == 0
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then getChainLengthRec next (length + 1)
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else length + nextLength
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numOfLoops :: Integer -> Integer -> Integer
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numOfLoops bound length = foldr (\n num -> num + if getChainLength n == length then 1 else 0) 0 [3..bound]
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main = print $ numOfLoops 1000000 60
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