Data update

Task/Recamans-sequence/Haskell/recamans-sequence-2.hs

@@ -1,42 +1,8 @@
-import Data.Set (Set, fromList, insert, isSubsetOf, member, size)
-import Data.Bool (bool)
-
-firstNRecamans :: Int -> [Int]
-firstNRecamans n = reverse $ recamanUpto (\(_, i, _) -> n == i)
-
-firstDuplicateR :: Int
-firstDuplicateR = head $ recamanUpto (\(rs, _, set) -> size set /= length rs)
-
-recamanSuperset :: Set Int -> [Int]
-recamanSuperset setInts =
-  tail $ recamanUpto (\(_, _, setR) -> isSubsetOf setInts setR)
-
-recamanUpto :: (([Int], Int, Set Int) -> Bool) -> [Int]
-recamanUpto p = rs
-  where
-    (rs, _, _) =
-      until
-        p
-        (\(rs@(r:_), i, seen) ->
-            let n = nextR seen i r
-            in (n : rs, succ i, insert n seen))
-        ([0], 1, fromList [0])
-
-nextR :: Set Int -> Int -> Int -> Int
-nextR seen i r =
-  let back = r - i
-  in bool back (r + i) (0 > back || member back seen)
-
--- TEST ---------------------------------------------------------------
-main :: IO ()
-main =
-  (putStrLn . unlines)
-    [ "First 15 Recamans:"
-    , show $ firstNRecamans 15
-    , []
-    , "First duplicated Recaman:"
-    , show firstDuplicateR
-    , []
-    , "Length of Recaman series required to include [0..1000]:"
-    , (show . length . recamanSuperset) $ fromList [0 .. 1000]
-    ]
+recaman :: Integer -> [Integer]
+recaman n = reverse (go 0 0 [])
+            where
+                go i a_n xs | i > n    = xs
+                            | (am > 0) && (not (any (am ==) xs)) = go (i + 1) am (am : xs)
+                            | otherwise = go (i + 1) ap (ap : xs)
+                            where  am =  a_n - (i + 1)
+                                   ap =  a_n + (i + 1)