Consecutive primes with ascending or descending differences: Difference between revisions
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(→{{header|Haskell}}: added solution) |
m (→{{header|Haskell}}: Removed a typo (trailing W prevented compilation after `primes`) added explicit module import) |
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=={{header|Haskell}}== |
=={{header|Haskell}}== |
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Uses prime generator implemented in the [[Sieve_of_Eratosthenes#Improved_efficiency_Wheels]]. |
Uses prime generator implemented in the [[Sieve_of_Eratosthenes#Improved_efficiency_Wheels]]. |
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<lang haskell>import Data.Numbers.Primes |
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consecutives equiv = filter ((> 1) . length) . go [] |
consecutives equiv = filter ((> 1) . length) . go [] |
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where |
where |
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go (y:ys) (h:t) | y `equiv` h = go (h:y:ys) t |
go (y:ys) (h:t) | y `equiv` h = go (h:y:ys) t |
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| otherwise = (y:ys) : go [h] t |
| otherwise = (y:ys) : go [h] t |
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-- finds maximal values in a list and returns the first one |
-- finds maximal values in a list and returns the first one |
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maximumBy g (h:t) = foldr f h t |
maximumBy g (h:t) = foldr f h t |
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where f r x = if g r < g x then x else r |
where f r x = if g r < g x then x else r |
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-- the task implementation |
-- the task implementation |
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task ord n = reverse $ p+s : p : (fst <$> rest) |
task ord n = reverse $ p+s : p : (fst <$> rest) |
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$ consecutives (\(_,a) (_,b) -> a `ord` b) |
$ consecutives (\(_,a) (_,b) -> a `ord` b) |
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$ differences |
$ differences |
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$ takeWhile (< n) |
$ takeWhile (< n) primes |
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differences l = zip l $ zipWith (-) (tail l) l</lang> |
differences l = zip l $ zipWith (-) (tail l) l</lang> |
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