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  1. import Data.List (sortBy)
  2. import Data.Function (on)
  3.  
  4. permutationBetween' l1@(h1:t) l2 =
  5.     case span (/= (False, h1)) l2 of
  6.          (prefix, (False, h2):r) ->
  7.              length prefix : permutationBetween' t (prefix ++ [(True, h2)] ++ r)
  8.          (prefix, []) -> error "Uh oh"
  9. permutationBetween' _ _ = []
  10.  
  11. permutationBetween ::  Eq a1 => [a1] -> [a1] -> [Int]
  12. permutationBetween l1 l2 = permutationBetween' l1 $ map ((,) False) l2
  13.  
  14. permute indices list = map (list !!) indices
  15.  
  16. data Color = Red | Blue | Green | Yellow
  17.     deriving (Eq, Show)
  18.  
  19. main = do
  20.     let source = [Red, Red, Green, Blue]
  21.     let target = [Blue, Red, Green, Red]
  22.     let perm = permutationBetween source target
  23.     putStrLn $ "Source:\t" ++ show source
  24.     putStrLn $ "Target:\t" ++ show target
  25.     putStrLn $ "Permutation:\t" ++ show perm
  26.     let restore = permute perm
  27.     putStrLn $ "Restored source:\t" ++ show (restore target)
Success #stdin #stdout 0.02s 3544KB
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Standard input is empty
stdout
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Source:	[Red,Red,Green,Blue]
Target:	[Blue,Red,Green,Red]
Permutation:	[1,3,2,0]
Restored source:	[Red,Red,Green,Blue]
https://ideone.com/kzSoCE
language:
Haskell (ghc 8.4.4)
created:
11 years ago
visibility:
secret

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