Consecutive primes with ascending or descending differences: Difference between revisions
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m (→{{header|Haskell}}: Removed a typo (trailing W prevented compilation after `primes`) added explicit module import) |
m (→{{header|Haskell}}: Specified import expression) |
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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 |
<lang haskell>import Data.Numbers.Primes (primes) |
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-- generates consecutive subsequences defined by given equivalence relation |
-- generates consecutive subsequences defined by given equivalence relation |
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where |
where |
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go r [] = [r] |
go r [] = [r] |
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go [] (h:t) = go [h] t |
go [] (h : t) = go [h] t |
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go (y:ys) (h |
go (y : ys) (h : t) |
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| y `equiv` h = go (h : y : ys) t |
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| 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 |
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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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where |
where |
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(p,s):rest = |
(p, s) : rest = |
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maximumBy length $ |
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$ consecutives (\(_,a) (_,b) -> a `ord` b) |
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consecutives (\(_, a) (_, b) -> a `ord` b) $ |
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differences $ |
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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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