33 lines
934 B
Haskell
33 lines
934 B
Haskell
-- module Main where
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import Data.IntSet (size)
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import Data.List (unfoldr)
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import Math.NumberTheory.ArithmeticFunctions (divisorsSmall)
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main :: IO ()
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main = print ans
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-- triangleNumber :: Integer -> [Integer]
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-- triangleNumber 1 = [1]
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-- triangleNumber n = sum [1..n] : triangleNumber (n-1)
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triangleNumber i = (i * (i + 1)) `div` 2
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triangleNumbers = map triangleNumber [1..]
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-- triangleNumbers :: [Int]
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-- triangleNumbers = unfoldr (\b-> Just (sum [1..b],b+1)) 1
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-- isDivisible a b = a `rem` b == 0
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-- divisors n = filter (isDivisible n) [1..(floor . sqrt) n ]
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-- Triangle Numbers With More than N divisors
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tnwmtNd :: Int -> [Int]
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tnwmtNd n = filter ((>= n) . size . divisorsSmall) triangleNumbers
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ans :: Int
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ans = head $ tnwmtNd 500
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{-
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λ> main
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76576500
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(0.00 secs, 114,944 bytes)
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First triangle number to have over 500 divisors is 76576500
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-}
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