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@flq flq/Permutation.hs
Last active Aug 29, 2015

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No-frills permutation code in Haskell
module Permutation where
permutate :: [a] -> [[a]]
permutate [x1,x2] = [[x1,x2],[x2,x1]]
permutate items = concat $ map p $ getEachInFrontOnce items
where
p (x:xs) = map (\items -> [x]++items) $ permutate xs
getEachInFrontOnce items = map (putItemAtIndexToFront items) [0..length items-1]
putItemAtIndexToFront items idx = [items!!idx] ++ take idx items ++ drop (idx+1) items
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