all tasks

Task/Topswops/Haskell/topswops-1.hs

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+import Data.List (permutations)
+
+topswops :: Int -> Int
+topswops n = maximum $ map tops $ permutations [1 .. n]
+    where
+        tops    (1 : _) = 0
+        tops xa@(x : _) = 1 + tops reordered
+            where
+                reordered = reverse (take x xa) ++ drop x xa
+
+main = mapM_
+        (\x -> putStrLn $ show x ++ ":\t" ++ show (topswops x))
+        [1 .. 10]

Task/Topswops/Haskell/topswops-2.hs

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+import Data.List
+import Control.Arrow
+import Control.Monad
+
+derangements [1] = [[1]]
+derangements xs = filter (and . zipWith (/=) [1..] ). permutations $ xs
+topswop = ((uncurry (++). first reverse).). splitAt
+topswopIter = takeWhile((/=1).head). iterate (topswop =<< head)
+swops =  map (length. topswopIter). derangements
+
+topSwops :: [Int] -> [(Int, Int)]
+topSwops = zip [1..]. map (maximum. swops). drop 1. inits