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jadlr/ListPermutations.hs

Last active February 22, 2016 11:06
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Permutations of a certain length of a list in haskell (v2)
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ListPermutations.hs
module ListPermutations where
listPermutations :: [a] -> Integer -> [[a]]
listPermutations _ 0 = [[]]
listPermutations [] _ = []
listPermutations (x:xs) n = fmap (x:) (listPermutations xs (n - 1)) ++ listPermutations xs n
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jadlr commented Feb 22, 2016

lazy, so this returns immediately:

*ListPermutations> take 2 $ listPermutations [1..1000] 15
[[1,2,3,4,5,6,7,8,9,10],[1,2,3,4,5,6,7,8,9,11]]

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lwld commented Feb 22, 2016

👍

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