27 lines
724 B
Haskell
27 lines
724 B
Haskell
-- 145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.
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--
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-- Find the sum of all numbers which are equal to the sum of the factorial of their digits.
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--
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-- Note: as 1! = 1 and 2! = 2 are not sums they are not included.
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import Data.Char
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factorial :: (Integral a) => a -> a
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factorial 0 = 1
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factorial n = n * factorial (n - 1)
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factDigits :: [Int]
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factDigits = map factorial [0 .. 9]
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equalsDigitFactorial :: Int -> Bool
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equalsDigitFactorial n =
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let fact_digit_sum = sum $ [factDigits !! x | x <- map digitToInt (show n)]
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in fact_digit_sum == n
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main = do
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let result = sum $ filter equalsDigitFactorial [10 .. 9999999]
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putStrLn $
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"Project Euler, Problem 34\n"
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++ "Answer: "
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++ show result
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