35 lines
895 B
Haskell
35 lines
895 B
Haskell
{-
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https://projecteuler.net/problem=1
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If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9.
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The sum of these multiples is 23.
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Find the sum of all the multiples of 3 or 5 below 1000.
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-}
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{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
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{-# HLINT ignore "Use sum" #-}
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module Main where
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main :: IO ()
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main = print ans
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ans :: Integer
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ans = sum $ allNumbersUnder 1000
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sum' :: Num a => [a] -> a
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sum' = foldl (+) 0
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isMultipleOf :: Integral a => a -> a -> Bool
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isMultipleOf n x = x `rem` n == 0
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all3sUnder :: Integral a => a -> [a]
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all3sUnder n = filter (isMultipleOf 3) [1..n-1]
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all5sUnder :: Integral a => a -> [a]
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all5sUnder n = filter (isMultipleOf 5) [1..n-1]
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allXsUnderN :: Integral a => a -> a -> [a]
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allXsUnderN x n = filter (isMultipleOf x) [1..n-1]
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allNumbersUnder :: Integral a => a -> [a]
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allNumbersUnder l = allXsUnderN 3 l <> allXsUnderN 5 l
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