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September 2017 Update

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Ingy döt Net 2017-09-23 10:01:46 +02:00
parent bba7bfd280
commit ba8067c3b7
14570 changed files with 153136 additions and 63871 deletions
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21
Task/Permutations-by-swapping/Haskell/permutations-by-swapping.hs
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@ -1,14 +1,15 @@
s_permutations :: [a] -> [([a], Int)]
s_permutations = flip zip (cycle [1, -1]) . (foldl aux [[]])
where aux items x = do
(f,item) <- zip (cycle [reverse,id]) items
f (insertEv x item)
insertEv x [] = [[x]]
insertEv x l@(y:ys) = (x:l) : map (y:) (insertEv x ys)
sPermutations :: [a] -> [([a], Int)]
sPermutations = flip zip (cycle [-1, 1]) . foldr aux [[]]
where
aux x items = do
(f, item) <- zip (repeat id) items
f (insertEv x item)
insertEv x [] = [[x]]
insertEv x l@(y:ys) = (x : l) : ((y :) <$> insertEv x ys)
main :: IO ()
main = do
putStrLn "3 items:"
mapM_ print $ s_permutations [0..2]
putStrLn "4 items:"
mapM_ print $ s_permutations [0..3]
mapM_ print $ sPermutations [1 .. 3]
putStrLn "\n4 items:"
mapM_ print $ sPermutations [1 .. 4]