Partition function P: Difference between revisions
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→{{header|Haskell}}: Applied Ormolu
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=={{header|Haskell}}==
<lang haskell>{-#
------------------------------------------------------------
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data Memo a = Node a (Memo a) (Memo a)
deriving (Functor
memo :: Integral a => Memo p -> a -> p
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nats :: Memo Int
nats =
nats = Node 0 ((+1).(*2) <$> nats) ((*2).(+1) <$> nats)▼
Node
0
((+ 1) . (* 2) <$> nats)
------------------------------------------------------------
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| otherwise = sum $ zipWith (*) signs terms
where
terms =
[ memo partitions (n
| i <- takeWhile (<= n) ofsets
signs = cycle [1,1,-1,-1]▼
]
▲ signs = cycle [1, 1, -1, -1]
ofsets
ofsets = scanl1 (+) $ mix [1, 3 ..] [1, 2 ..]
where
mix a b = concat $ zipWith (\x y -> [x, y]) a b
main :: IO ()
main = print $ partitionP 6666</lang>
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